Javafx vm opções

Software Engineer Sandbox.
Esta publicação é uma cheatsheet com enumeração de opções, que sempre deve ser usada para configurar o Java Virtual Machine para aplicações de servidor orientadas para a Web (ou seja, Web Front-End) em ambientes de produção ou de produção.
Para a listagem completa dos leitores preguiçosos está aqui (para explicação detalhada curiosa é fornecida abaixo):
Faça do Servidor um Servidor.
Transforma os recursos da Java VM específicos para aplicativos do servidor, como o compilador JIT sofisticado. Embora esta opção esteja implicitamente habilitada para máquinas virtuais x64, ainda faz sentido usá-lo, de acordo com o comportamento da documentação, talvez alterado no futuro.
Faça o seu Heap Explicit.
Para evitar redimensionamento dinâmico e atrasos, o que pode ser causado por isso, especificamos explicitamente o tamanho mínimo e máximo do heap. Assim, a Java VM passará o tempo apenas uma vez para se comprometer em todo o heap.
A lógica para a geração permanente é a mesma que para o dimensionamento geral do tamanho da pilha - predefina para evitar custos de mudanças dinâmicas. Não aplicável a Java & gt; = 8.
Por padrão, o Metaspace em Java VM 8 não é limitado, porém, por uma questão de estabilidade do sistema, faz sentido limitá-lo com algum valor finito.
Definir explicitamente o tamanho da geração jovem.
Ratio que determina o tamanho do espaço de sobrevivência relativamente ao tamanho eden. A relação pode ser calculada usando a seguinte fórmula:
Faça o GC Direito.
Como o tempo de resposta é crítico para a aplicação do servidor, os fatores concorrentes concorrentes são melhores para aplicativos da Web. Desafortunadamente, o G1 ainda não está pronto para produção, portanto, temos que usar coletor concorrente Mark-Sweep.
Por padrão, o CMS GC usa um conjunto de regras heurísticas para desencadear a coleta de lixo. Isso torna o GC menos previsível e geralmente tende a atrasar a coleta até a geração antiga estar quase ocupada. Iniciá-lo antecipadamente permite completar a coleção antes que a geração antiga esteja cheia e, assim, evitar o GC completo (ou seja, a pausa para o mundo). - XX: + UseCMSInitiatingOccupancyOnly impedir o uso de heurísticas GC. - XX: CMSInitiatingOccupancyFraction informa Java VM quando CMS deve ser acionado. Basicamente, ele permite criar um buffer em heap, que pode ser preenchido com dados, enquanto o CMS está funcionando. Assim, o percentual deve ser calculado de volta da velocidade na qual a memória é consumida em geração antiga durante a carga de produção. Esses percentuais devem ser escolhidos com cuidado, se ele for pequeno - o CMS funcionará com freqüência, se for grande - o CMS será desencadeado muito tarde e a falha no modo concorrente pode ocorrer. Geralmente - XX: CMSInitiatingOccupancyFraction deve estar no nível 70, o que significa que o aplicativo deve utilizar menos que 70% da geração anterior.
Instrui o colector de lixo a colecionar a geração jovem antes de fazer a fase de observação completa do GC ou do CMS e, como resultado, melhorar seu desempenho devido à ausência de necessidade de verificar as referências entre geração jovem e tenured.
Registro de GC.
Essas opções tornam o Java a registrar as atividades do coletor de lixo no arquivo especificado. Todos os registros serão antecipados com data e hora legíveis por humanos. Enquanto isso, você deve evitar usar - XX: + PrintGCTimeStamps, pois irá pré-gravar registro com timestamp inútil desde o início do aplicativo Java.
Gerar log pode ser posteriormente analisado com o GCViewer.
A rotação de arquivos de log do GC faz a análise dos problemas de coleta de lixo mais fácil, também garante que o disco está protegido do consumo excessivo de espaço.
Cache DNS.
Número de segundos durante os quais o registro DNS será armazenado em cache na VM Java. O comportamento padrão do Java VM 6 era armazenar em cache para sempre, o que não requer o uso do servidor do pé, pois você não gostaria de reiniciar o servidor sempre que o IP mudasse no registro DNS. Ele foi alterado em Java VM 7 para armazenar em cache por 30 segundos, mas somente se o Gerenciador de segurança não estiver instalado. Dependendo da versão da VM Java e da presença de gerenciadores de segurança, os registros DNS ainda podem ser armazenados em cache infinitamente.
A opção comummente recomendada é desativar o cache de DNS, o que pode ser motivo de degradação do desempenho. Os pedidos ao DNS são realizados em blocos sincronizados e apenas uma solicitação é realizada em qualquer ponto no tempo. Assim, se o seu aplicativo estiver usando uma rede, ele experimentará saturação em pedidos de DNS, portanto, o valor TTL 0 nunca deve ser usado.
Uma melhor solução é armazenar em cache por um período razoável não longo, por exemplo, 1 minuto (60 segundos). Isso significa que o sistema em que seu aplicativo está interagindo tem que garantir que dois IPs diferentes continuarão a funcionar corretamente durante este 1 minuto, caso contrário, o valor TTL inferior deve ser escolhido. Deve sempre ser razoável (não igual a 0) para evitar possíveis contenções de pedidos para o DNS.
Esta opção é conveniente para uso, mas networkaddress. cache. ttl especificado em% JRE% / lib / security / java. security deve ser considerado como uma solução melhor, pelo menos a partir de documentação oficial prospectiva.
Dump on Out of Memory.
Se o seu aplicativo falharia sempre com a falta de memória na produção, você não gostaria de esperar por outra chance de reproduzir o problema. Essas opções indicam a Java VM para despejar a memória no arquivo, quando o OOM ocorreu. Pode causar pausas consideráveis ​​em grandes montes durante o evento OOM. No entanto, se Java VM estiver no OOM já, coletar tanta informação sobre o problema é mais importante do que tentar servir o tráfego com um aplicativo completamente quebrado. Também estamos certificando-se de que o despejo seria criado com o nome exclusivo por hora de início da aplicação (isso é requeired porque Java VM falhará para substituir o arquivo existente).
Faça o JMX funcionar.
Endereço IP, que seria incorporado em stubs RMI enviados aos clientes. Clientes posteriores usarão esses stubs para se comunicarem com o servidor via RMI. Como na máquina moderna de datacenters, muitas vezes tem dois IPs (internos e externos), você quer especificar explicitamente qual IP usar, caso contrário a JVM fará sua própria escolha. O valor correto dessa propriedade é uma condição prévia para usar com sucesso o JMX.
A opção - Dcom. sun. management. jmxremote não é necessária a partir do Java VM 6, no entanto, para tornar o JMX disponível para acesso remoto, a porta de escuta específica deve ser fornecida. Mais tarde, esta porta pode ser usada para se conectar usando qualquer ferramenta JMX (por exemplo, VisualVM ou Java Mission Control).
Também para reduzir problemas adicionais com a conexão, desabilite a autenticação padrão, mas certifique-se de que apenas usuários autorizados possam se conectar ao ambiente usando o firewall. Se, por razões de segurança, você ainda quiser controlar o acesso via mecanismo padrão, aprenda mais.
Muitas opções que anteriormente eram muito úteis com atualizações em Java VM (especificamente lançamento de Java 7) são pré-configuradas por padrão:

Opções Javafx vm
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Como posso configurar as opções de VM em um Projeto Modular da plataforma Java Netbeans?
Eu tenho um projeto modular da plataforma Netbeans, não um projeto Java regular. Eu quero definir opções de VM para aumentar a memória, mas na caixa de diálogo "propriedades", não há como fazer isso para um projeto de plataforma modular da Netbeans. Isso me custou grandes quantidades de tempo e ainda não encontrei uma boa maneira de configurar os args VM.
Alguém sabe como configurar VM args usando um projeto modular da plataforma Netbeans, ao compilar e executar o programa no Netbeans 7? Dada a quantidade de problemas, estou quase pronto para desistir da Netbeans para criar aplicativos modulares.
É bastante fácil, na verdade. Basta modificar o arquivo project. properties para incluir a seguinte linha:
Claro, você pode incluir outras opções JVM lá.
O que fiz foi modificar o arquivo project. properties, como JB disse, mas a maneira correta de fazê-lo foi adicionar um - J antes dos args. Por exemplo.,
Isso fez isso! Não tenho certeza por que levou 3 meses para descobrir isso. Definitivamente, uma falha na documentação do Netbeans. Eles realmente deveriam fazer isso editável no menu de propriedades, em vez de fazer caçar usuários através de arquivos de configuração sem memória.
Eu pensei que iria colocar alguma contribuição sobre este tópico, Quando eu estava desenvolvendo um aplicativo de plataforma netbeans eu também enfrentei o mesmo problema, eu adicionei run. args. extra = - J-Xmx768m e atualizei meu arquivo project. properties, mas didn ' t! Mas quando eu adicionei run. args. extra = - J-Xmx768m no meu arquivo platform. properties, então funcionou, isso só funciona quando eu estava em um ambiente de desenvolvimento. Quando eu empacotei o aplicativo para o Windows, o problema permaneceu o mesmo, meu tamanho de pilha mínima era 24m e o máximo é de 64m. Então eu descobri que, se eu atualizar e adicionar default_options = "- branding my_project - J-Xms64m - J-Xmx1G" em my_project. conf no meu diretório instalado C: \ Arquivos de Programas \ meu_projeto \ etc, então execute meu aplicativo e verifiquei o log log agora posso ver a mudança. Dessa forma, não tive a sorte de ver até o nó executado quando clicar direito e acessar o diálogo de propriedades do projeto no netbeans 7.0.1. É a equipe de sonhos up to netbeans para nos fazer sentir com sorte.
Eu tive esse problema e, depois de alguns cavando e lendo muitos documentos, consegui deduzir que a maioria desses valores eram provenientes de modelos no arnês.
Então, se você for no seu IDE_home / harness / etc / você encontrará o arquivo "app. conf". Este arquivo é renomeado durante uma compilação de distro e o "app. conf" torna-se seu "nome de aplicativo. conf". Edite este arquivo com os valores padrão que você gostaria em seu aplicativo.
No meu caso, substituí a linha que dizia: default_options = "- branding $ - J-Xms24m - Xmx64m" com default_options = "- branding $ - J-Xms64m - Xmx512m", pois meu aplicativo estava precisando de mais memória. Ao alterar o modelo, não tenho que tocar em todas as implementações e mudar a CLI da memória para a VM.
Espero que isto ajude!
Para projetos de maven:
Conforme descrito nesta pergunta, você pode usar o parâmetro etcConfFile do nbm-maven-plugin:
Você deve adicionar essas linhas ao arquivo de propriedades do projeto.
Se você quiser usar o Netbeans para definir as opções de VM sem se preocupar com qual arquivo editar, aqui vamos:
Adicione sua opção na caixa de texto correspondente, por exemplo: - Xms10m.

Opções de Java HotSpot VM.
Observe que esta página se aplica apenas ao JDK 7 e versões anteriores. Para o JDK 8, veja as páginas de referência do Windows, Solaris, Linux e Mac OS X.
Este documento fornece informações sobre as opções típicas da linha de comando e as variáveis ​​de ambiente que podem afetar as características de desempenho da máquina virtual Java HotSpot. Salvo indicação em contrário, todas as informações contidas neste documento pertencem ao Java HotSpot Client VM e ao Java HotSpot Server VM.
Categorias de opções Java HotSpot Java.
As opções padrão reconhecidas pela Java HotSpot VM são descritas nas páginas de referência do Java Application Launcher para Windows e Solaris & amp; Linux. Este documento trata exclusivamente de opções não padrão reconhecidas pelo Java HotSpot VM:
As opções que começam com - X não são padrão (não é garantida para serem suportadas em todas as implementações da VM) e estão sujeitas a alterações sem aviso prévio nas versões subseqüentes do JDK. As opções especificadas com - XX não são estáveis ​​e estão sujeitas a alterações sem aviso prévio. Os usuários de JDKs anteriores a 1.3.0 que desejam acessar uma VM de Java HotSpot, devem ver os Equivalentes Java HotSpot de Sinalizadores da VM Exata.
Algumas opções úteis - XX.
Os valores padrão são listados para Java SE 6 para Solaris Sparc com o servidor. Algumas opções podem variar de acordo com a arquitetura / OS / JVM. Plataformas com um valor padrão diferente estão listadas na descrição.
As opções booleanas estão ativadas com - XX: + & lt; opção & gt; e desligou com - XX: - & lt; option & gt; As opções Numero Numérico são definidas com - XX: & lt; option & gt; = & lt; number & gt; . Os números podem incluir 'm' ou 'M' para megabytes, 'k' ou 'K' para kilobytes e 'g' ou 'G' para gigabytes (por exemplo, 32k é o mesmo que 32768). As opções de seqüência de caracteres são definidas com - XX: & lt; opção & gt; = & lt; string & gt; , geralmente são usados ​​para especificar um arquivo, um caminho ou uma lista de comandos.
As bandeiras marcadas como gerenciáveis ​​são graváveis ​​de forma dinâmica através da interface de gerenciamento JDK (com. sun. management. HotSpotDiagnosticMXBean API) e também através do JConsole. No monitoramento e gerenciamento de Java SE 6 Platform Applications, a Figura 3 mostra um exemplo. As bandeiras gerenciáveis ​​também podem ser definidas através de jinfo-flag.
Opções comportamentais.
Garbage First (G1) Opções de coleta de lixo.
Opções de desempenho.
0 - nenhuma instrução de prefetch é gerar * d *,
1 - execute instruções de pré-seleção após cada alocação,
2 - use o ponteiro de marca de água da alocação TLAB para o portão quando as instruções de pré-seleção são executadas.

Configurando as opções da JVM e as propriedades da plataforma.
Opções JVM.
A maneira recomendada de alterar as opções da JVM nas versões recentes do produto é da Ajuda | Edite o menu Opções de VM personalizadas. Esta ação criará uma cópia do arquivo. vmoptions no diretório de configuração IDE e abrirá um editor onde você pode alterá-los. Se você não pode iniciar o IDE para acessar este menu, edite o arquivo manualmente conforme descrito abaixo.
As opções de VM são carregadas a partir do arquivo IDE_HOME \ bin \ & lt; product & gt; [bits] [.exe].vmoptions ou da cópia deste arquivo no diretório config (se existir). Observe que o arquivo. vmoptions do diretório de configuração tem prioridade sobre o arquivo original no diretório bin.
As opções são definidas uma por linha:
Se você estiver executando a JVM de 64 bits (verifique em Ajuda | Sobre), as opções devem ser editadas no arquivo com 64 sufixos em seu nome (idea64.exe. vmoptions ou idea64.vmoptions no Linux, mas sempre ideia. Mac). O produto seria um dos seguintes: idéia, phpstorm, webstorm, pycharm, rubymine, appcode. - Xmx valor limita o tamanho da memória de heap máximo que a JVM pode alocar.
Para as personalizações para sobreviver às atualizações, copie o arquivo para o diretório de configuração do IDE e, em seguida, modifique a cópia em vez do original.
Mac OS X Specifics.
Não edite arquivos. vmoptions e. properties diretamente, ele irá violar a assinatura do aplicativo, sempre faça uma cópia dos arquivos no diretório de configuração IDE e edite a cópia em vez disso. Veja esta resposta para obter detalhes. O arquivo original está localizado na pasta /Applications/<Product>.app/Contents/bin (/Applications/<Product>.app/bin para versões IDE mais antigas).
Propriedades da plataforma IntelliJ IDEA.
A maneira recomendada de alterar as propriedades da plataforma nas versões recentes do produto é da Ajuda | Editar menu Propriedades personalizadas. Esta ação criará uma cópia do arquivo. properties no diretório de configuração IDE e abrirá um editor onde você pode alterá-los. Se você não pode iniciar o IDE para acessar este menu, edite o arquivo manualmente conforme descrito abaixo.
Você pode alterar as propriedades no arquivo IDE_HOME \ bin \ idea. properties para todos os produtos, algumas propriedades populares que você deseja ajustar:
Para as personalizações para sobreviver às atualizações, copie o arquivo para o diretório de configuração do IDE e, em seguida, modifique a cópia em vez do original.
Esse artigo foi útil?
Claro que você precisará executar seu editor de texto como administrador se estiver editando arquivos no Windows 7-Program Files.
Oi Adolfo! Essas configurações são para o quê? tornar o IntelliJ mais rápido ou qual o propósito? Obrigado!
Raul, as configurações comportamentais e de desempenho são especificamente combinadas para atender minha máquina e o tipo de projetos com os quais estou trabalhando. Algumas dessas bandeiras estão obsoletas ou alteradas com o java 8. você pode ler mais sobre as bandeiras na documentação:
Adolfo Quais as propriedades recomendadas para a ideia 14, testei estas e reduzi substancialmente o tempo de inicialização.
Ou apenas copie a idéia. Impressiona as coisas de lá para aqui.
Alejandrodazal Eu uso mais ou menos as mesmas configurações, mas como eu mencionei para Raul, se você estiver usando o java 8 você precisa controlar suas bandeiras (PermGen para Metaspace)
no OSX, você precisa alterar o valor do seu & lt; key & gt; JVMVersion & lt; / key & gt; para usar java 8 com & lt; string & gt; 1.8 * & lt; / string & gt;
Obrigado pelo lembrete do MetaSpace. esqueceu tudo sobre desaparecimento de permgen.
Esta é uma ótima informação. Alguém atualizou as opções / configurações originais da Adolfo para as versões mais recentes dos IDEs?
Qual é a configuração ideal para o arquivo e por que não é mais fácil de configurar? Se quisermos brincar com ele durante a vida útil do produto.
O link para "IDE Configuration Directory" está quebrado.
Acabei de atualizar para 2016.1.
Pacotes de Programas (x86) - & gt; JetBrains - & gt; IntelliJ IDEA 2016.1 - & gt; bin - & gt; idea64.exe. vmoptions está lá onde deveria ser.
O programa ainda não começará com a caixa de diálogo.
"Erro ao iniciar o IDEA. Não é possível encontrar o arquivo de opções VM"
Todd eu tive o mesmo problema e foi porque eu estava tentando usar o atalho para a versão anterior. Acabei de marcar o novo atalho que foi criado e agora funciona. Não tenho certeza se este é o mesmo problema que você está tendo.
A configuração que faz com que isso não seja iniciada em 2016.1 é esta:
Remova e tudo funciona bem.
oi, no IntelliJ IDEA 2016.1.1 e jdk1.8.0_77 e wondows7 O MetaspaceSize não funciona. porque? me ajude, muito obrigado.
Como você sabe que isso não funciona? O que você espera que aconteça?
Por que exibir tamanho metapace 1.078G, eu configurei MaxMetaspaceSize = 350m, por que? Obrigado.
Você pode verificar idea. log (intellij-support. jetbrains / hc / articles / 207241085) para ver se essas opções foram aplicadas a partir do seu arquivo personalizado. vmoptions. Se fosse, o resto depende da VM. Caso a VM não respeite esta opção, envie um erro para a Oracle.
Obrigado por sua resposta.
Parece que as opções foram aplicadas, mas isso não funciona.
Para Mac OS X, ** NÃO ** faça sua própria cópia de idea64.vmoptions. Basta usar a Ajuda - & gt; Editar opções de VM personalizadas. Isso fará a cópia para você.
Tive problemas quando criei idea64.vmoptions por mim (por este artigo) e usei o menu Ajuda para editá-lo. Tudo salva OK, mas minhas novas opções de VM ainda não estavam sendo usadas. Eu exclui o novo arquivo de idea64.vmoptions e comecei novamente do zero, e parece que finalmente está funcionando. Posso finalmente usar o IntelliJ em "tempo real" novamente :-)
Eu escrevi um guia sobre o github que explica muitas dessas bandeiras e o que elas fazem. Qualquer um que visite esta página para orientação de desempenho, dê uma olhada e contribua se você tiver algum conhecimento!

Opções Javafx vm
Lança um aplicativo Java.
Opções de linha de comando separadas por espaços. Veja Opções.
O nome da classe a ser lançada.
O nome do arquivo Java Archive (JAR) deve ser chamado. Usado apenas com a opção - jar.
Os argumentos passaram para o método main () separado por espaços.
Descrição.
O comando java inicia uma aplicação Java. Ele faz isso iniciando o Java Runtime Environment (JRE), carregando a classe especificada e chamando o método principal () da classe. O método deve ser declarado público e estático, ele não deve retornar nenhum valor, e ele deve aceitar uma matriz String como um parâmetro. A declaração do método tem o seguinte formulário:
O comando java pode ser usado para iniciar uma aplicação JavaFX carregando uma classe que tenha um método main () ou que estenda o javafx. application. Application. No último caso, o iniciador constrói uma instância da classe Application, chama seu método init () e, em seguida, chama o método start (javafx. stage. Stage).
Por padrão, o primeiro argumento que não é uma opção do comando java é o nome totalmente qualificado da classe a ser chamada. Se a opção - jar for especificada, seu argumento é o nome do arquivo JAR que contém arquivos de classe e recurso para o aplicativo. A classe de inicialização deve ser indicada pelo cabeçalho do manifesto da Classe Principal no seu código fonte.
O JRE procura a classe de inicialização (e outras classes usadas pelo aplicativo) em três conjuntos de locais: o caminho da classe bootstrap, as extensões instaladas e o caminho da classe do usuário.
Argumentos após o nome do arquivo da classe ou o nome do arquivo JAR são passados ​​para o método main ().
O comando javaw é idêntico ao java, exceto que com javaw não há janela de console associada. Use javaw quando você não deseja que uma janela de prompt de comando apareça. O javaw launcher, no entanto, exibirá uma caixa de diálogo com informações de erro se um lançamento falhar.
O comando java suporta uma ampla gama de opções que podem ser divididas nas seguintes categorias:
As opções padrão são garantidas para serem suportadas por todas as implementações da Java Virtual Machine (JVM). Eles são usados ​​para ações comuns, como verificar a versão do JRE, definir o caminho da classe, ativar a saída detalhada e assim por diante.
As opções não padrão são opções de propósito geral que são específicas do Java HotSpot Virtual Machine, portanto, elas não são garantidas para serem suportadas por todas as implementações da JVM e estão sujeitas a alterações. Essas opções começam com - X.
As opções avançadas não são recomendadas para uso casual. Estas são as opções do desenvolvedor usadas para ajustar áreas específicas da operação da Máquina Virtual Java HotSpot que geralmente possuem requisitos específicos do sistema e podem exigir acesso privilegiado aos parâmetros de configuração do sistema. Também não são garantidos para serem suportados por todas as implementações JVM, e estão sujeitos a alterações. As opções avançadas começam com - XX.
Para acompanhar as opções que foram obsoletas ou removidas na versão mais recente, há uma seção chamada Opções desativadas e removidas no final do documento.
As opções booleanas são usadas para ativar um recurso desativado por padrão ou desativar um recurso habilitado por padrão. Tais opções não requerem um parâmetro. As opções Boolean - XX são habilitadas usando o sinal de mais (-XX: + OptionName) e desabilitadas usando o sinal de menos (-XX: - OptionName).
Para as opções que exigem um argumento, o argumento pode ser separado do nome da opção por um espaço, dois-pontos (:) ou um sinal igual (=), ou o argumento pode seguir diretamente a opção (a sintaxe exata difere para cada opção ). Se for esperado que especifique o tamanho em bytes, você não pode usar nenhum sufixo, ou use o sufixo k ou K para kilobytes (KB), m ou M para megabytes (MB), g ou G para gigabytes (GB). Por exemplo, para definir o tamanho para 8 GB, você pode especificar 8g, 8192m, 8388608k ou 8589934592 como o argumento. Se for esperado que especifique a porcentagem, use um número de 0 a 1 (por exemplo, especifique 0,25 para 25%).
Opções padrão.
Estas são as opções mais usadas que são suportadas por todas as implementações da JVM.
Carrega a biblioteca de agentes nativos especificada. Após o nome da biblioteca, uma lista separada por vírgulas de opções específicas para a biblioteca pode ser usada.
Se a opção - agentlib: foo for especificada, a JVM tentará carregar a biblioteca chamada foo. dll no local especificado pela variável do sistema PATH.
O exemplo a seguir mostra como carregar a biblioteca da ferramenta de perfilamento amplo (HPROF) e obter informações de amostra da CPU a cada 20 ms, com uma profundidade de pilha de 3:
O exemplo a seguir mostra como carregar a biblioteca Java Debug Wire Protocol (JDWP) e ouvir a conexão do soquete na porta 8000, suspendendo a JVM antes da carga da classe principal:
Para obter mais informações sobre as bibliotecas de agentes nativos, consulte o seguinte:
Carrega a biblioteca do agente nativo especificada pelo nome do caminho absoluto. Esta opção é equivalente a - agentlib, mas usa o caminho completo e o nome do arquivo da biblioteca.
Seleciona o Java HotSpot Client VM. A versão de 64 bits do Java SE Development Kit (JDK) atualmente ignora esta opção e, em vez disso, usa a JVM do Servidor.
Para a seleção de JVM padrão, veja Detecção de máquina de Classe de Servidor em.
Define um valor de propriedade do sistema. A variável de propriedade é uma string sem espaços que representa o nome da propriedade. A variável de valor é uma string que representa o valor da propriedade. Se o valor for uma string com espaços, envie-a entre aspas (por exemplo, - Dfoo = "foo bar").
-disableassertions [: [packagename]. |: classname] - da [: [packagename]. |: classname]
Desativa as afirmações. Por padrão, as afirmações são desabilitadas em todos os pacotes e classes.
Sem argumentos, - disableassertions (-da) desativa asserções em todos os pacotes e classes. Com o argumento do nome do pacote terminando em. , o interruptor desativa as asserções no pacote especificado e em quaisquer subpacotes. Se o argumento é simplesmente. , então a chave desativa as asserções no pacote sem nome no diretório de trabalho atual. Com o argumento classname, a chave desabilita asserções na classe especificada.
A opção - disableassertions (-da) aplica-se a todos os carregadores de classe e a classes de sistema (que não possuem um carregador de classe). Há uma exceção para esta regra: se a opção for fornecida sem argumentos, não se aplica às classes do sistema. Isso facilita a desativação de asserções em todas as classes, exceto para classes de sistema. A opção - disablesystemassertions permite que você desative as afirmações em todas as classes do sistema.
Para ativar explicitamente asserções em pacotes ou classes específicas, use a opção - enableassertions (-ea). Ambas as opções podem ser usadas ao mesmo tempo. Por exemplo, para executar o aplicativo MyClass com asserções habilitadas no pacote com. wombat. fruitbat (e quaisquer subpacotes), mas desabilitado na classe com. wombat. fruitbat. Brickbat, use o seguinte comando:
Desativa asserções em todas as classes do sistema.
-enableassertions [: [packagename]. |: classname] - ea [: [packagename]. |: classname]
Permite asserções. Por padrão, as afirmações são desabilitadas em todos os pacotes e classes.
Sem argumentos, - enableassertions (-ea) permite asserções em todos os pacotes e classes. Com o argumento do nome do pacote terminando em. , o interruptor permite asserções no pacote especificado e em quaisquer subpacotes. Se o argumento é simplesmente. , então a opção permite asserções no pacote sem nome no diretório de trabalho atual. Com o argumento classname, a opção permite asserções na classe especificada.
A opção - enableassertions (-ea) aplica-se a todos os carregadores de classe e às classes do sistema (que não possuem um carregador de classe). Há uma exceção para esta regra: se a opção for fornecida sem argumentos, não se aplica às classes do sistema. Isso facilita a habilitação das asserções em todas as classes, exceto para as classes do sistema. A opção - enablesystemassertions fornece uma opção separada para permitir asserções em todas as classes do sistema.
Para desativar explicitamente as afirmações em pacotes ou classes específicas, use a opção - disableassertions (-da). Se um único comando contém várias instâncias dessas opções, elas serão processadas antes de carregar qualquer classe. Por exemplo, para executar o aplicativo MyClass com asserções ativadas somente no pacote com. wombat. fruitbat (e quaisquer subpacotes), mas desabilitado na classe com. wombat. fruitbat. Brickbat, use o seguinte comando:
Permite asserções em todas as classes do sistema.
Exibe informações de uso para o comando java sem realmente executar a JVM.
Executa um programa encapsulado em um arquivo JAR. O argumento do nome do arquivo é o nome de um arquivo JAR com um manifesto que contém uma linha no formulário Classe principal: classname que define a classe com o método public static void main (String [] args) que serve como ponto de partida do seu aplicativo.
Quando você usa a opção - jar, o arquivo JAR especificado é a fonte de todas as classes de usuário e outras configurações de caminho de classe são ignoradas.
Para obter mais informações sobre arquivos JAR, consulte os seguintes recursos:
Lição: Programas de Embalagem em Arquivos JAR em.
Carrega o agente de linguagem de programação Java especificado. Para obter mais informações sobre a instrumentação de aplicativos Java, consulte a descrição do pacote java. lang. instrument na documentação da API Java em docs. oracle/javase/8/docs/api/java/lang/instrument/package-summary. html.
Inclui JREs user-private na pesquisa de versão.
Exclui JREs usuário-privado da pesquisa de versão.
Seleciona o Java HotSpot Server VM. A versão de 64 bits do JDK suporta apenas a VM do Servidor, então, nesse caso, a opção está implícita.
Para a seleção de JVM padrão, veja Detecção de máquina de Classe de Servidor em.
Exibe informações de versão e continua a execução do aplicativo. Esta opção é equivalente à opção de versão, exceto que o último instrui a JVM a sair depois de exibir as informações da versão.
Mostra a tela inicial com a imagem especificada pelo imgname. Por exemplo, para mostrar o arquivo splash. gif do diretório de imagens ao iniciar seu aplicativo, use a seguinte opção:
Exibe informações sobre cada classe carregada.
Exibe informações sobre cada evento de coleta de lixo (GC).
Exibe informações sobre o uso de métodos nativos e outras atividades Java Native Interface (JNI).
Exibe informações de versão e depois sai. Esta opção é equivalente à opção - showversion, exceto que o último não instrui a JVM a sair depois de exibir as informações da versão.
Especifica a versão de lançamento a ser usada para executar o aplicativo. Se a versão do comando java chamada não atender a esta especificação e uma implementação apropriada for encontrada no sistema, a implementação apropriada será usada.
O argumento de lançamento especifica a seqüência de versão exata, ou uma lista de cadeias de versão e intervalos separados por espaços. Uma seqüência de versão é a designação do desenvolvedor do número da versão da seguinte forma: 1. x .0_ u (onde x é o número de versão principal e u é o número da versão de atualização). Um intervalo de versão é composto por uma seqüência de versão seguida por um sinal de mais (+) para designar esta versão ou posterior, ou uma parte de uma seqüência de versão seguida de um asterisco (*) para designar qualquer string de versão com um prefixo correspondente. As cadeias de caracteres e os intervalos das versões podem ser combinados usando um espaço para uma combinação OU lógica ou um e comercial (& amp;) para uma combinação AND lógica de duas cadeias / intervalos de versão. Por exemplo, se a execução da classe ou do arquivo JAR requer JRE 6u13 (1.6.0_13) ou qualquer JRE 6 a partir de 6u10 (1.6.0_10), especifique o seguinte:
As citações são necessárias apenas se houver espaços no parâmetro de lançamento.
Para arquivos JAR, a preferência é especificar requisitos de versão no manifesto do arquivo JAR e não na linha de comando.
Opções não-padrão.
Essas opções são opções de propósito geral que são específicas da máquina virtual Java HotSpot.
Exibe a ajuda para todas as opções - X disponíveis.
Desativa a compilação de fundo. Por padrão, a JVM compila o método como uma tarefa em segundo plano, executando o método no modo intérprete até que a compilação de fundo seja concluída. A bandeira - Xbatch desabilita a compilação de fundo para que a compilação de todos os métodos prosseguir como uma tarefa de primeiro plano até ser concluída.
Esta opção é equivalente a - XX: - BackgroundCompilation.
Especifica uma lista de diretórios, arquivos JAR e arquivos ZIP separados por ponto e vírgula (;) para procurar arquivos de classe de inicialização. Estes são usados ​​no lugar dos arquivos de classe de inicialização incluídos no JDK.
Não implante aplicativos que usam essa opção para substituir uma classe em rt. jar, pois isso viola a licença de código binário JRE.
Especifica uma lista de diretórios, arquivos JAR e arquivos ZIP separados por ponto e vírgula (;) para anexar ao final do caminho de classe de inicialização padrão.
Não implante aplicativos que usam essa opção para substituir uma classe em rt. jar, pois isso viola a licença de código binário JRE.
Especifica uma lista de diretórios, arquivos JAR e arquivos ZIP separados por ponto-e-vírgula (;) para se antecipar à frente do caminho de classe de inicialização padrão.
Não implante aplicativos que usam essa opção para substituir uma classe em rt. jar, pois isso viola a licença de código binário JRE.
Executa verificações adicionais para funções Java Native Interface (JNI). Especificamente, ele valida os parâmetros passados ​​para a função JNI e os dados do ambiente de tempo de execução antes de processar a solicitação JNI. Qualquer dado inválido encontrado indica um problema no código nativo e a JVM terminará com um erro irrecuperável em tais casos. Espere uma degradação de desempenho quando esta opção for usada.
Força a compilação de métodos na primeira invocação. By default, the Client VM ( - client ) performs 1,000 interpreted method invocations and the Server VM ( - server ) performs 10,000 interpreted method invocations to gather information for efficient compilation. Specifying the - Xcomp option disables interpreted method invocations to increase compilation performance at the expense of efficiency.
You can also change the number of interpreted method invocations before compilation using the - XX:CompileThreshold option.
Does nothing. Provided for backward compatibility.
Shows additional diagnostic messages.
Enables strict class-file format checks that enforce close conformance to the class-file format specification. Developers are encouraged to use this flag when developing new code because the stricter checks will become the default in future releases.
Runs the application in interpreted-only mode. Compilation to native code is disabled, and all bytecode is executed by the interpreter. The performance benefits offered by the just in time (JIT) compiler are not present in this mode.
Displays more detailed JVM version information than the - version option, and then exits.
Sets the file to which verbose GC events information should be redirected for logging. The information written to this file is similar to the output of - verbose:gc with the time elapsed since the first GC event preceding each logged event. The - Xloggc option overrides - verbose:gc if both are given with the same java command.
Specifies the maximum code cache size (in bytes) for JIT-compiled code. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option - XX:-TieredCompilation , then the default size is 48 MB:
This option is equivalent to - XX:ReservedCodeCacheSize .
Executes all bytecode by the interpreter except for hot methods, which are compiled to native code.
Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
The young generation region of the heap is used for new objects. GC is performed in this region more often than in other regions. If the size for the young generation is too small, then a lot of minor garbage collections will be performed. If the size is too large, then only full garbage collections will be performed, which can take a long time to complete. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size.
The following examples show how to set the initial and maximum size of young generation to 256 MB using various units:
Instead of the - Xmn option to set both the initial and maximum size of the heap for the young generation, you can use - XX:NewSize to set the initial size and - XX:MaxNewSize to set the maximum size.
Sets the initial size (in bytes) of the heap. This value must be a multiple of 1024 and greater than 1 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
The following examples show how to set the size of allocated memory to 6 MB using various units:
If you do not set this option, then the initial size will be set as the sum of the sizes allocated for the old generation and the young generation. The initial size of the heap for the young generation can be set using the - Xmn option or the - XX:NewSize option.
Specifies the maximum size (in bytes) of the memory allocation pool in bytes. This value must be a multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is chosen at runtime based on system configuration. For server deployments, - Xms and - Xmx are often set to the same value. See the section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection Tuning Guide at docs. oracle/javase/8/docs/technotes/guides/vm/gctuning/index. html .
The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
The - Xmx option is equivalent to - XX:MaxHeapSize .
Disables garbage collection (GC) of classes. This can save some GC time, which shortens interruptions during the application run.
When you specify - Xnoclassgc at startup, the class objects in the application will be left untouched during GC and will always be considered live. This can result in more memory being permanently occupied which, if not used carefully, will throw an out of memory exception.
Profiles the running program and sends profiling data to standard output. This option is provided as a utility that is useful in program development and is not intended to be used in production systems.
Reduces the use of operating system signals by the JVM.
Shutdown hooks enable orderly shutdown of a Java application by running user cleanup code (such as closing database connections) at shutdown, even if the JVM terminates abruptly.
The JVM watches for console control events to implement shutdown hooks for unexpected termination. Specifically, the JVM registers a console control handler that begins shutdown-hook processing and returns TRUE for CTRL_C_EVENT , CTRL_CLOSE_EVENT , CTRL_LOGOFF_EVENT , and CTRL_SHUTDOWN_EVENT .
The JVM uses a similar mechanism to implement the feature of dumping thread stacks for debugging purposes. The JVM uses CTRL_BREAK_EVENT to perform thread dumps.
If the JVM is run as a service (for example, as a servlet engine for a web server), then it can receive CTRL_LOGOFF_EVENT but should not initiate shutdown because the operating system will not actually terminate the process. To avoid possible interference such as this, the - Xrs option can be used. When the - Xrs option is used, the JVM does not install a console control handler, implying that it does not watch for or process CTRL_C_EVENT , CTRL_CLOSE_EVENT , CTRL_LOGOFF_EVENT , or CTRL_SHUTDOWN_EVENT .
There are two consequences of specifying - Xrs :
Ctrl + Break thread dumps are not available.
User code is responsible for causing shutdown hooks to run, for example, by calling System. exit() when the JVM is to be terminated.
Sets the class data sharing (CDS) mode. Possible mode arguments for this option include the following:
Use CDS if possible. This is the default value for Java HotSpot 32-Bit Client VM.
Require the use of CDS. Print an error message and exit if class data sharing cannot be used.
Do not use CDS. This is the default value for Java HotSpot 32-Bit Server VM, Java HotSpot 64-Bit Client VM, and Java HotSpot 64-Bit Server VM.
Manually generate the CDS archive. Specify the application class path as described in "Setting the Class Path".
You should regenerate the CDS archive with each new JDK release.
Shows settings and continues. Possible category arguments for this option include the following:
Shows all categories of settings. This is the default value.
Shows settings related to locale.
Shows settings related to system properties.
Shows the settings of the JVM.
Sets the thread stack size (in bytes). Append the letter k or K to indicate KB, m or M to indicate MB, g or G to indicate GB. The default value depends on virtual memory.
The following examples set the thread stack size to 1024 KB in different units:
This option is equivalent to - XX:ThreadStackSize .
Sets the mode of the bytecode verifier. Bytecode verification ensures that class files are properly formed and satisfy the constraints listed in section 4.10, Verification of class Files in the The Java Virtual Machine Specification .
Do not turn off verification as this reduces the protection provided by Java and could cause problems due to ill-formed class files.
Possible mode arguments for this option include the following:
Verifies all bytecodes not loaded by the bootstrap class loader. This is the default behavior if you do not specify the - Xverify option.
Enables verification of all bytecodes.
Disables verification of all bytecodes. Use of - Xverify:none is unsupported.
Advanced Runtime Options.
These options control the runtime behavior of the Java HotSpot VM.
Enables the option to prevent the java command from running a Java application if it uses the endorsed-standards override mechanism or the extension mechanism. This option checks if an application is using one of these mechanisms by checking the following:
The java. ext. dirs or java. endorsed. dirs system property is set.
The lib/endorsed directory exists and is not empty.
The lib/ext directory contains any JAR files other than those of the JDK.
The system-wide platform-specific extension directory contains any JAR files.
Enables the option that disables the mechanism that lets tools attach to the JVM. By default, this option is disabled, meaning that the attach mechanism is enabled and you can use tools such as jcmd , jstack , jmap , and jinfo .
Specifies the path and file name to which error data is written when an irrecoverable error occurs. By default, this file is created in the current working directory and named hs_err_pid pid. log where pid is the identifier of the process that caused the error. The following example shows how to set the default log file (note that the identifier of the process is specified as %p ):
The following example shows how to set the error log file to C:/log/java/java_error. log :
If the file cannot be created in the specified directory (due to insufficient space, permission problem, or another issue), then the file is created in the temporary directory for the operating system. The temporary directory is specified by the value of the TMP environment variable; if that environment variable is not defined, then the value of the TEMP environment variable is used.
Enables automatic failover to the old verifier when the new type checker fails. By default, this option is disabled and it is ignored (that is, treated as disabled) for classes with a recent bytecode version. You can enable it for classes with older versions of the bytecode.
Enables the use of the Java Flight Recorder (JFR) during the runtime of the application. This is a commercial feature that works in conjunction with the - XX:+UnlockCommercialFeatures option as follows:
If this option is not provided, Java Flight Recorder can still be enabled in a running JVM by providing the appropriate jcmd diagnostic commands.
Disables the use of the Java Flight Recorder (JFR) during the runtime of the application. This is a commercial feature that works in conjunction with the - XX:+UnlockCommercialFeatures option as follows:
If this option is provided, Java Flight Recorder cannot be enabled in a running JVM.
Sets the parameters that control the behavior of JFR. This is a commercial feature that works in conjunction with the - XX:+UnlockCommercialFeatures option. This option can be used only when JFR is enabled (that is, the - XX:+FlightRecorder option is specified).
The following list contains all available JFR parameters:
Specifies whether the recording is a continuous background recording or if it runs for a limited time. By default, this parameter is set to false (recording runs for a limited time). To make the recording run continuously, set the parameter to true .
Specifies whether JFR should write a continuous recording to disk. By default, this parameter is set to false (continuous recording to disk is disabled). To enable it, set the parameter to true , and also set defaultrecording=true .
Specifies whether a dump file of JFR data should be generated when the JVM terminates in a controlled manner. By default, this parameter is set to false (dump file on exit is not generated). To enable it, set the parameter to true , and also set defaultrecording=true .
The dump file is written to the location defined by the dumponexitpath parameter.
Specifies the path and name of the dump file with JFR data that is created when the JVM exits in a controlled manner if you set the dumponexit=true parameter. Setting the path makes sense only if you also set defaultrecording=true .
If the specified path is a directory, the JVM assigns a file name that shows the creation date and time. If the specified path includes a file name and if that file already exists, the JVM creates a new file by appending the date and time stamp to the specified file name.
Specifies the total amount of primary memory (in bytes) used for data retention. Append k or K , to specify the size in KB, m or M to specify the size in MB, g or G to specify the size in GB. By default, the size is set to 462848 bytes.
Specify the amount of data written to the log file by JFR. By default, it is set to info .
Specifies the maximum age of disk data to keep for the default recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 30s means 30 seconds). By default, the maximum age is set to 15 minutes ( 15m ).
This parameter is valid only if you set the disk=true parameter.
Specifies the maximum size (in bytes) of the data chunks in a recording. Append k or K , to specify the size in KB, m or M to specify the size in MB, g or G to specify the size in GB. By default, the maximum size of data chunks is set to 12 MB.
Specifies the maximum size (in bytes) of disk data to keep for the default recording. Append k or K , to specify the size in KB, m or M to specify the size in MB, g or G to specify the size in GB. By default, the maximum size of disk data is not limited, and this parameter is set to 0.
This parameter is valid only if you set the disk=true parameter.
Specifies the repository (a directory) for temporary disk storage. By default, the system's temporary directory is used.
Specifies whether thread sampling is enabled. Thread sampling occurs only if the sampling event is enabled along with this parameter. By default, this parameter is enabled.
Specifies the path and name of the event settings file (of type JFC). By default, the default. jfc file is used, which is located in JAVA_HOME/jre/lib/jfr .
Stack depth for stack traces by JFR. By default, the depth is set to 64 method calls. The maximum is 2048, minimum is 1.
Specifies the per-thread local buffer size (in bytes). Append k or K , to specify the size in KB, m or M to specify the size in MB, g or G to specify the size in GB. Higher values for this parameter allow more data gathering without contention to flush it to the global storage. It can increase application footprint in a thread-rich environment. By default, the local buffer size is set to 5 KB.
You can specify values for multiple parameters by separating them with a comma. For example, to instruct JFR to write a continuous recording to disk, and set the maximum size of data chunks to 10 MB, specify the following:
On Solaris, sets the maximum size (in bytes) for large pages used for Java heap. The size argument must be a power of 2 (2, 4, 8, 16, . ). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically.
The following example illustrates how to set the large page size to 4 megabytes (MB):
Sets the maximum total size (in bytes) of the New I/O (the java. nio package) direct-buffer allocations. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the size is set to 0, meaning that the JVM chooses the size for NIO direct-buffer allocations automatically.
The following examples illustrate how to set the NIO size to 1024 KB in different units:
Specifies the mode for tracking JVM native memory usage. Possible mode arguments for this option include the following:
Do not track JVM native memory usage. This is the default behavior if you do not specify the - XX:NativeMemoryTracking option.
Only track memory usage by JVM subsystems, such as Java heap, class, code, and thread.
In addition to tracking memory usage by JVM subsystems, track memory usage by individual CallSite , individual virtual memory region and its committed regions.
Sets the memory alignment of Java objects (in bytes). By default, the value is set to 8 bytes. The specified value should be a power of two, and must be within the range of 8 and 256 (inclusive). This option makes it possible to use compressed pointers with large Java heap sizes.
The heap size limit in bytes is calculated as:
Note: As the alignment value increases, the unused space between objects will also increase. As a result, you may not realize any benefits from using compressed pointers with large Java heap sizes.
Sets a custom command or a series of semicolon-separated commands to run when an irrecoverable error occurs. If the string contains spaces, then it must be enclosed in quotation marks.
The following example shows how the - XX:OnError option can be used to run the userdump. exe utility to obtain a crash dump in case of an irrecoverable error (the %p designates the current process):
The preceding example assumes that the path to the userdump. exe utility is specified in the PATH environment variable.
Sets a custom command or a series of semicolon-separated commands to run when an OutOfMemoryError exception is first thrown. If the string contains spaces, then it must be enclosed in quotation marks. For an example of a command string, see the description of the - XX:OnError option.
If enabled, saves jstat (1) binary data when the Java application exits. This binary data is saved in a file named hsperfdata_ <pid> , where <pid> is the process identifier of the Java application you ran. Use jstat to display the performance data contained in this file as follows:
Enables printing of ergonomically selected JVM flags that appeared on the command line. It can be useful to know the ergonomic values set by the JVM, such as the heap space size and the selected garbage collector. By default, this option is disabled and flags are not printed.
Enables printing of collected native memory tracking data at JVM exit when native memory tracking is enabled (see - XX:NativeMemoryTracking ). By default, this option is disabled and native memory tracking data is not printed.
Decreases the amount of access control checks in the verifier. By default, this option is disabled, and it is ignored (that is, treated as disabled) for classes with a recent bytecode version. You can enable it for classes with older versions of the bytecode.
Enables the use of Resource Management during the runtime of the application.
This is a commercial feature that requires you to also specify the - XX:+UnlockCommercialFeatures option as follows:
java - XX:+UnlockCommercialFeatures - XX:+ResourceManagement.
Sets the parameter that controls the sampling interval for Resource Management measurements, in milliseconds.
This option can be used only when Resource Management is enabled (that is, the - XX:+ResourceManagement option is specified).
Specifies the path and name of the class data sharing (CDS) archive file.
Specifies the text file that contains the names of the class files to store in the class data sharing (CDS) archive. This file contains the full name of one class file per line, except slashes ( / ) replace dots ( . ). For example, to specify the classes java. lang. Object and hello. Main , create a text file that contains the following two lines:
The class files that you specify in this text file should include the classes that are commonly used by the application. They may include any classes from the application, extension, or bootstrap class paths.
Enables displaying of a dialog box when the JVM experiences an irrecoverable error. This prevents the JVM from exiting and keeps the process active so that you can attach a debugger to it to investigate the cause of the error. By default, this option is disabled.
Starts a JFR recording for the Java application. This is a commercial feature that works in conjunction with the - XX:+UnlockCommercialFeatures option. This option is equivalent to the JFR. start diagnostic command that starts a recording during runtime. You can set the following parameters when starting a JFR recording:
Specifies whether to compress the JFR recording log file (of type JFR) on the disk using the gzip file compression utility. This parameter is valid only if the filename parameter is specified. By default it is set to false (recording is not compressed). To enable compression, set the parameter to true .
Specifies whether the recording is a continuous background recording or if it runs for a limited time. By default, this parameter is set to false (recording runs for a limited time). To make the recording run continuously, set the parameter to true .
Specifies the delay between the Java application launch time and the start of the recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 10m means 10 minutes). By default, there is no delay, and this parameter is set to 0.
Specifies whether a dump file of JFR data should be generated when the JVM terminates in a controlled manner. By default, this parameter is set to false (dump file on exit is not generated). To enable it, set the parameter to true .
The dump file is written to the location defined by the filename parameter.
Specifies the duration of the recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 5h means 5 hours). By default, the duration is not limited, and this parameter is set to 0.
Specifies the path and name of the JFR recording log file.
Specifies the identifier for the JFR recording. By default, it is set to Recording x .
Specifies the maximum age of disk data to keep for the default recording. Append s to specify the time in seconds, m for minutes, h for hours, or d for days (for example, specifying 30s means 30 seconds). By default, the maximum age is set to 15 minutes ( 15m ).
Specifies the maximum size (in bytes) of disk data to keep for the default recording. Append k or K , to specify the size in KB, m or M to specify the size in MB, g or G to specify the size in GB. By default, the maximum size of disk data is not limited, and this parameter is set to 0.
Specifies the path and name of the event settings file (of type JFC). By default, the default. jfc file is used, which is located in JAVA_HOME/jre/lib/jfr .
You can specify values for multiple parameters by separating them with a comma. For example, to save the recording to test. jfr in the current working directory, and instruct JFR to compress the log file, specify the following:
Sets the thread stack size (in bytes). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value depends on virtual memory.
The following examples show how to set the thread stack size to 1024 KB in different units:
This option is equivalent to - Xss .
Enables tracing of classes as they are loaded. By default, this option is disabled and classes are not traced.
Enables tracing of all loaded classes in the order in which they are referenced. By default, this option is disabled and classes are not traced.
Enables tracing of constant pool resolutions. By default, this option is disabled and constant pool resolutions are not traced.
Enables tracing of classes as they are unloaded. By default, this option is disabled and classes are not traced.
Enables tracing of the loader constraints recording. By default, this option is disabled and loader constraints recording is not traced.
Enables the use of commercial features. Commercial features are included with Oracle Java SE Advanced or Oracle Java SE Suite packages, as defined on the Java SE Products page at oracle/technetwork/java/javase/terms/products/index. html.
By default, this option is disabled and the JVM runs without the commercial features. Once they were enabled for a JVM process, it is not possible to disable their use for that process.
If this option is not provided, commercial features can still be unlocked in a running JVM by using the appropriate jcmd diagnostic commands.
Enables application class data sharing (AppCDS). To use AppCDS, you must also specify values for the options - XX:SharedClassListFile and - XX:SharedArchiveFile during both CDS dump time (see the option - Xshare:dump ) and application run time.
This is a commercial feature that requires you to also specify the - XX:+UnlockCommercialFeatures option. This is also an experimental feature; it may change in future releases.
Disables the use of biased locking. Some applications with significant amounts of uncontended synchronization may attain significant speedups with this flag enabled, whereas applications with certain patterns of locking may see slowdowns. For more information about the biased locking technique, see the example in Java Tuning White Paper at oracle/technetwork/java/tuning-139912.html#section4.2.5.
By default, this option is enabled.
Disables the use of compressed pointers. By default, this option is enabled, and compressed pointers are used when Java heap sizes are less than 32 GB. When this option is enabled, object references are represented as 32-bit offsets instead of 64-bit pointers, which typically increases performance when running the application with Java heap sizes less than 32 GB. This option works only for 64-bit JVMs.
It is also possible to use compressed pointers when Java heap sizes are greater than 32GB. See the - XX:ObjectAlignmentInBytes option.
Enables the use of large page memory. By default, this option is disabled and large page memory is not used.
For more information, see "Large Pages".
Enables issuing of membars on thread state transitions. This option is disabled by default on all platforms except ARM servers, where it is enabled. (It is recommended that you do not disable this option on ARM servers.)
Enables the perfdata feature. This option is enabled by default to allow JVM monitoring and performance testing. Disabling it suppresses the creation of the hsperfdata_userid directories. To disable the perfdata feature, specify - XX:-UsePerfData .
Enables installation of signal handlers by the application. By default, this option is disabled and the application is not allowed to install signal handlers.
Advanced JIT Compiler Options.
These options control the dynamic just-in-time (JIT) compilation performed by the Java HotSpot VM.
Enables the use of aggressive performance optimization features, which are expected to become default in upcoming releases. By default, this option is disabled and experimental performance features are not used.
Sets the number of lines to prefetch ahead of the instance allocation pointer. By default, the number of lines to prefetch is set to 1:
Only the Java HotSpot Server VM supports this option.
Sets the size (in bytes) of the prefetch distance for object allocation. Memory about to be written with the value of new objects is prefetched up to this distance starting from the address of the last allocated object. Each Java thread has its own allocation point.
Negative values denote that prefetch distance is chosen based on the platform. Positive values are bytes to prefetch. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is set to -1.
The following example shows how to set the prefetch distance to 1024 bytes:
Only the Java HotSpot Server VM supports this option.
Sets the prefetch instruction to prefetch ahead of the allocation pointer. Only the Java HotSpot Server VM supports this option. Possible values are from 0 to 3. The actual instructions behind the values depend on the platform. By default, the prefetch instruction is set to 0:
Only the Java HotSpot Server VM supports this option.
Sets the number of cache lines to load after the last object allocation by using the prefetch instructions generated in compiled code. The default value is 1 if the last allocated object was an instance, and 3 if it was an array.
The following example shows how to set the number of loaded cache lines to 5:
Only the Java HotSpot Server VM supports this option.
Sets the step size (in bytes) for sequential prefetch instructions. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the step size is set to 16 bytes:
Only the Java HotSpot Server VM supports this option.
Sets the generated code style for prefetch instructions. The style argument is an integer from 0 to 3:
Do not generate prefetch instructions.
Execute prefetch instructions after each allocation. This is the default parameter.
Use the thread-local allocation block (TLAB) watermark pointer to determine when prefetch instructions are executed.
Use BIS instruction on SPARC for allocation prefetch.
Only the Java HotSpot Server VM supports this option.
Enables background compilation. This option is enabled by default. To disable background compilation, specify - XX:-BackgroundCompilation (this is equivalent to specifying - Xbatch ).
Sets the number of compiler threads to use for compilation. By default, the number of threads is set to 2 for the server JVM, to 1 for the client JVM, and it scales to the number of cores if tiered compilation is used. The following example shows how to set the number of threads to 2:
Sets the minimum free space (in bytes) required for compilation. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. When less than the minimum free space remains, compiling stops. By default, this option is set to 500 KB. The following example shows how to set the minimum free space to 1024 MB:
Specifies a command to perform on a method. For example, to exclude the indexOf() method of the String class from being compiled, use the following:
Note that the full class name is specified, including all packages and subpackages separated by a slash ( / ). For easier cut and paste operations, it is also possible to use the method name format produced by the - XX:+PrintCompilation and - XX:+LogCompilation options:
If the method is specified without the signature, the command will be applied to all methods with the specified name. However, you can also specify the signature of the method in the class file format. In this case, you should enclose the arguments in quotation marks, because otherwise the shell treats the semicolon as command end. For example, if you want to exclude only the indexOf(String) method of the String class from being compiled, use the following:
You can also use the asterisk (*) as a wildcard for class and method names. For example, to exclude all indexOf() methods in all classes from being compiled, use the following:
The commas and periods are aliases for spaces, making it easier to pass compiler commands through a shell. You can pass arguments to - XX:CompileCommand using spaces as separators by enclosing the argument in quotation marks:
Note that after parsing the commands passed on the command line using the - XX:CompileCommand options, the JIT compiler then reads commands from the. hotspot_compiler file. You can add commands to this file or specify a different file using the - XX:CompileCommandFile option.
To add several commands, either specify the - XX:CompileCommand option multiple times, or separate each argument with the newline separator ( \n ). The following commands are available:
Set a breakpoint when debugging the JVM to stop at the beginning of compilation of the specified method.
Exclude all methods from compilation except for the specified method. As an alternative, you can use the - XX:CompileOnly option, which allows to specify several methods.
Prevent inlining of the specified method.
Exclude the specified method from compilation.
Print a help message for the - XX:CompileCommand option.
Attempt to inline the specified method.
Exclude compilation logging (with the - XX:+LogCompilation option) for all methods except for the specified method. By default, logging is performed for all compiled methods.
This command can be used to pass a JIT compilation option to the specified method in place of the last argument ( option ). The compilation option is set at the end, after the method name. For example, to enable the BlockLayoutByFrequency option for the append() method of the StringBuffer class, use the following:
You can specify multiple compilation options, separated by commas or spaces.
Print generated assembler code after compilation of the specified method.
Do not print the compile commands. By default, the commands that you specify with the - XX:CompileCommand option are printed; for example, if you exclude from compilation the indexOf() method of the String class, then the following will be printed to standard output:
You can suppress this by specifying the - XX:CompileCommand=quiet option before other - XX:CompileCommand options.
Sets the file from which JIT compiler commands are read. By default, the. hotspot_compiler file is used to store commands performed by the JIT compiler.
Each line in the command file represents a command, a class name, and a method name for which the command is used. For example, this line prints assembly code for the toString() method of the String class:
For more information about specifying the commands for the JIT compiler to perform on methods, see the - XX:CompileCommand option.
Sets the list of methods (separated by commas) to which compilation should be restricted. Only the specified methods will be compiled. Specify each method with the full class name (including the packages and subpackages). For example, to compile only the length() method of the String class and the size() method of the List class, use the following:
Note that the full class name is specified, including all packages and subpackages separated by a slash ( / ). For easier cut and paste operations, it is also possible to use the method name format produced by the - XX:+PrintCompilation and - XX:+LogCompilation options:
Although wildcards are not supported, you can specify only the class or package name to compile all methods in that class or package, as well as specify just the method to compile methods with this name in any class:
Sets the number of interpreted method invocations before compilation. By default, in the server JVM, the JIT compiler performs 10,000 interpreted method invocations to gather information for efficient compilation. For the client JVM, the default setting is 1,500 invocations. This option is ignored when tiered compilation is enabled; see the option - XX:+TieredCompilation . The following example shows how to set the number of interpreted method invocations to 5,000:
You can completely disable interpretation of Java methods before compilation by specifying the - Xcomp option.
Enables the use of escape analysis. This option is enabled by default. To disable the use of escape analysis, specify - XX:-DoEscapeAnalysis . Only the Java HotSpot Server VM supports this option.
Sets the initial code cache size (in bytes). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is set to 500 KB. The initial code cache size should be not less than the system's minimal memory page size. The following example shows how to set the initial code cache size to 32 KB:
Enables method inlining. This option is enabled by default to increase performance. To disable method inlining, specify - XX:-Inline .
Sets the maximum code size (in bytes) for compiled methods that should be inlined. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. Only compiled methods with the size smaller than the specified size will be inlined. By default, the maximum code size is set to 1000 bytes:
Enables logging of compilation activity to a file named hotspot. log in the current working directory. You can specify a different log file path and name using the - XX:LogFile option.
By default, this option is disabled and compilation activity is not logged. The - XX:+LogCompilation option has to be used together with the - XX:UnlockDiagnosticVMOptions option that unlocks diagnostic JVM options.
You can enable verbose diagnostic output with a message printed to the console every time a method is compiled by using the - XX:+PrintCompilation option.
Sets the maximum bytecode size (in bytes) of a method to be inlined. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the maximum bytecode size is set to 35 bytes:
Sets the maximum number of nodes to be used during single method compilation. By default, the maximum number of nodes is set to 65,000:
Sets the maximum bytecode size (in bytes) of a trivial method to be inlined. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. By default, the maximum bytecode size of a trivial method is set to 6 bytes:
Enables the optimization of String concatenation operations. This option is enabled by default. To disable the optimization of String concatenation operations, specify - XX:-OptimizeStringConcat . Only the Java HotSpot Server VM supports this option.
Enables printing of assembly code for bytecoded and native methods by using the external disassembler. so library. This enables you to see the generated code, which may help you to diagnose performance issues.
By default, this option is disabled and assembly code is not printed. The - XX:+PrintAssembly option has to be used together with the - XX:UnlockDiagnosticVMOptions option that unlocks diagnostic JVM options.
Enables verbose diagnostic output from the JVM by printing a message to the console every time a method is compiled. This enables you to see which methods actually get compiled. By default, this option is disabled and diagnostic output is not printed.
You can also log compilation activity to a file by using the - XX:+LogCompilation option.
Enables printing of inlining decisions. This enables you to see which methods are getting inlined.
By default, this option is disabled and inlining information is not printed. The - XX:+PrintInlining option has to be used together with the - XX:+UnlockDiagnosticVMOptions option that unlocks diagnostic JVM options.
Sets the maximum code cache size (in bytes) for JIT-compiled code. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default maximum code cache size is 240 MB; if you disable tiered compilation with the option - XX:-TieredCompilation , then the default size is 48 MB. This option has a limit of 2 GB; otherwise, an error is generated. The maximum code cache size should not be less than the initial code cache size; see the option - XX:InitialCodeCacheSize . This option is equivalent to - Xmaxjitcodesize .
The RTM abort ratio is specified as a percentage (%) of all executed RTM transactions. If a number of aborted transactions becomes greater than this ratio, then the compiled code will be deoptimized. This ratio is used when the - XX:+UseRTMDeopt option is enabled. The default value of this option is 50. This means that the compiled code will be deoptimized if 50% of all transactions are aborted.
RTM locking code will be retried, when it is aborted or busy, the number of times specified by this option before falling back to the normal locking mechanism. The default value for this option is 5. The - XX:UseRTMLocking option must be enabled.
Disables the use of tiered compilation. By default, this option is enabled. Only the Java HotSpot Server VM supports this option.
Enables hardware-based AES intrinsics for Intel, AMD, and SPARC hardware. Intel Westmere (2010 and newer), AMD Bulldozer (2011 and newer), and SPARC (T4 and newer) are the supported hardware. UseAES is used in conjunction with UseAESIntrinsics.
UseAES and UseAESIntrinsics flags are enabled by default and are supported only for Java HotSpot Server VM 32-bit and 64-bit. To disable hardware-based AES intrinsics, specify - XX:-UseAES - XX:-UseAESIntrinsics . For example, to enable hardware AES, use the following flags:
To support UseAES and UseAESIntrinsics flags for 32-bit and 64-bit use - server option to choose Java HotSpot Server VM. These flags are not supported on Client VM.
Enables flushing of the code cache before shutting down the compiler. This option is enabled by default. To disable flushing of the code cache before shutting down the compiler, specify - XX:-UseCodeCacheFlushing .
Enables checking of whether the card is already marked before updating the card table. This option is disabled by default and should only be used on machines with multiple sockets, where it will increase performance of Java applications that rely heavily on concurrent operations. Only the Java HotSpot Server VM supports this option.
Auto-tunes RTM locking depending on the abort ratio. This ratio is specified by - XX:RTMAbortRatio option. If the number of aborted transactions exceeds the abort ratio, then the method containing the lock will be deoptimized and recompiled with all locks as normal locks. This option is disabled by default. The - XX:+UseRTMLocking option must be enabled.
Generate Restricted Transactional Memory (RTM) locking code for all inflated locks, with the normal locking mechanism as the fallback handler. This option is disabled by default. Options related to RTM are only available for the Java HotSpot Server VM on x86 CPUs that support Transactional Synchronization Extensions (TSX).
RTM is part of Intel's TSX, which is an x86 instruction set extension and facilitates the creation of multithreaded applications. RTM introduces the new instructions XBEGIN , XABORT , XEND , and XTEST . The XBEGIN and XEND instructions enclose a set of instructions to run as a transaction. If no conflict is found when running the transaction, the memory and register modifications are committed together at the XEND instruction. The XABORT instruction can be used to explicitly abort a transaction and the XEND instruction to check if a set of instructions are being run in a transaction.
A lock on a transaction is inflated when another thread tries to access the same transaction, thereby blocking the thread that did not originally request access to the transaction. RTM requires that a fallback set of operations be specified in case a transaction aborts or fails. An RTM lock is a lock that has been delegated to the TSX's system.
RTM improves performance for highly contended locks with low conflict in a critical region (which is code that must not be accessed by more than one thread concurrently). RTM also improves the performance of coarse-grain locking, which typically does not perform well in multithreaded applications. (Coarse-grain locking is the strategy of holding locks for long periods to minimize the overhead of taking and releasing locks, while fine-grained locking is the strategy of trying to achieve maximum parallelism by locking only when necessary and unlocking as soon as possible.) Also, for lightly contended locks that are used by different threads, RTM can reduce false cache line sharing, also known as cache line ping-pong. This occurs when multiple threads from different processors are accessing different resources, but the resources share the same cache line. As a result, the processors repeatedly invalidate the cache lines of other processors, which forces them to read from main memory instead of their cache.
Enables hardware-based intrinsics for SHA crypto hash functions for SPARC hardware. UseSHA is used in conjunction with the UseSHA1Intrinsics , UseSHA256Intrinsics , and UseSHA512Intrinsics options.
The UseSHA and UseSHA*Intrinsics flags are enabled by default, and are supported only for Java HotSpot Server VM 64-bit on SPARC T4 and newer.
This feature is only applicable when using the sun. security. provider. Sun provider for SHA operations.
To disable all hardware-based SHA intrinsics, specify - XX:-UseSHA . To disable only a particular SHA intrinsic, use the appropriate corresponding option. For example: - XX:-UseSHA256Intrinsics .
Enables intrinsics for SHA-1 crypto hash function.
Enables intrinsics for SHA-224 and SHA-256 crypto hash functions.
Enables intrinsics for SHA-384 and SHA-512 crypto hash functions.
Enables the transformation of scalar operations into superword operations. This option is enabled by default. To disable the transformation of scalar operations into superword operations, specify - XX:-UseSuperWord . Only the Java HotSpot Server VM supports this option.
Advanced Serviceability Options.
These options provide the ability to gather system information and perform extensive debugging.
Enables the dumping of the Java heap to a file in the current directory by using the heap profiler (HPROF) when a java. lang. OutOfMemoryError exception is thrown. You can explicitly set the heap dump file path and name using the - XX:HeapDumpPath option. By default, this option is disabled and the heap is not dumped when an OutOfMemoryError exception is thrown.
Sets the path and file name for writing the heap dump provided by the heap profiler (HPROF) when the - XX:+HeapDumpOnOutOfMemoryError option is set. By default, the file is created in the current working directory, and it is named java_pid pid. hprof where pid is the identifier of the process that caused the error. The following example shows how to set the default file explicitly ( %p represents the current process identificator):
The following example shows how to set the heap dump file to C:/log/java/java_heapdump. log :
Sets the path and file name where log data is written. By default, the file is created in the current working directory, and it is named hotspot. log .
The following example shows how to set the log file to C:/log/java/hotspot. log :
Enables printing of a class instance histogram after a Control+Break event. By default, this option is disabled.
Setting this option is equivalent to running the jmap - histo command, or the jcmd pid GC. class_histogram command, where pid is the current Java process identifier.
Enables printing of java. util. concurrent locks after a Control+Break event. By default, this option is disabled.
Setting this option is equivalent to running the jstack - l command or the jcmd pid Thread. print - l command, where pid is the current Java process identifier.
Unlocks the options intended for diagnosing the JVM. By default, this option is disabled and diagnostic options are not available.
Advanced Garbage Collection Options.
These options control how garbage collection (GC) is performed by the Java HotSpot VM.
Enables Java heap optimization. This sets various parameters to be optimal for long-running jobs with intensive memory allocation, based on the configuration of the computer (RAM and CPU). By default, the option is disabled and the heap is not optimized.
Enables touching of every page on the Java heap during JVM initialization. This gets all pages into the memory before entering the main() method. The option can be used in testing to simulate a long-running system with all virtual memory mapped to physical memory. By default, this option is disabled and all pages are committed as JVM heap space fills.
Enables class unloading when using the concurrent mark-sweep (CMS) garbage collector. This option is enabled by default. To disable class unloading for the CMS garbage collector, specify - XX:-CMSClassUnloadingEnabled .
Sets the percentage of time (0 to 100) used to weight the current sample when computing exponential averages for the concurrent collection statistics. By default, the exponential averages factor is set to 25%. The following example shows how to set the factor to 15%:
Sets the percentage of the old generation occupancy (0 to 100) at which to start a CMS collection cycle. The default value is set to -1. Any negative value (including the default) implies that - XX:CMSTriggerRatio is used to define the value of the initiating occupancy fraction.
The following example shows how to set the occupancy fraction to 20%:
Enables scavenging attempts before the CMS remark step. By default, this option is disabled.
Sets the percentage (0 to 100) of the value specified by - XX:MinHeapFreeRatio that is allocated before a CMS collection cycle commences. The default value is set to 80%.
The following example shows how to set the occupancy fraction to 75%:
Sets the number of threads used for concurrent GC. The default value depends on the number of CPUs available to the JVM.
For example, to set the number of threads for concurrent GC to 2, specify the following option:
Enables the option that disables processing of calls to System. gc() . This option is disabled by default, meaning that calls to System. gc() are processed. If processing of calls to System. gc() is disabled, the JVM still performs GC when necessary.
Enables invoking of concurrent GC by using the System. gc() request. This option is disabled by default and can be enabled only together with the - XX:+UseConcMarkSweepGC option.
Enables invoking of concurrent GC by using the System. gc() request and unloading of classes during the concurrent GC cycle. This option is disabled by default and can be enabled only together with the - XX:+UseConcMarkSweepGC option.
Sets the size of the regions into which the Java heap is subdivided when using the garbage-first (G1) collector. The value can be between 1 MB and 32 MB. The default region size is determined ergonomically based on the heap size.
The following example shows how to set the size of the subdivisions to 16 MB:
Enables the printing of information about which regions are allocated and which are reclaimed by the G1 collector. By default, this option is disabled.
Sets the percentage of the heap (0 to 50) that is reserved as a false ceiling to reduce the possibility of promotion failure for the G1 collector. By default, this option is set to 10%.
The following example shows how to set the reserved heap to 20%:
Sets the initial size (in bytes) of the memory allocation pool. This value must be either 0, or a multiple of 1024 and greater than 1 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is chosen at runtime based on system configuration. See the section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection Tuning Guide at docs. oracle/javase/8/docs/technotes/guides/vm/gctuning/index. html .
The following examples show how to set the size of allocated memory to 6 MB using various units:
If you set this option to 0, then the initial size will be set as the sum of the sizes allocated for the old generation and the young generation. The size of the heap for the young generation can be set using the - XX:NewSize option.
Sets the initial survivor space ratio used by the throughput garbage collector (which is enabled by the - XX:+UseParallelGC and/or - XX:+UseParallelOldGC options). Adaptive sizing is enabled by default with the throughput garbage collector by using the - XX:+UseParallelGC and - XX:+UseParallelOldGC options, and survivor space is resized according to the application behavior, starting with the initial value. If adaptive sizing is disabled (using the - XX:-UseAdaptiveSizePolicy option), then the - XX:SurvivorRatio option should be used to set the size of the survivor space for the entire execution of the application.
The following formula can be used to calculate the initial size of survivor space (S) based on the size of the young generation (Y), and the initial survivor space ratio (R):
The 2 in the equation denotes two survivor spaces. The larger the value specified as the initial survivor space ratio, the smaller the initial survivor space size.
By default, the initial survivor space ratio is set to 8. If the default value for the young generation space size is used (2 MB), the initial size of the survivor space will be 0.2 MB.
The following example shows how to set the initial survivor space ratio to 4:
Sets the percentage of the heap occupancy (0 to 100) at which to start a concurrent GC cycle. It is used by garbage collectors that trigger a concurrent GC cycle based on the occupancy of the entire heap, not just one of the generations (for example, the G1 garbage collector).
By default, the initiating value is set to 45%. A value of 0 implies nonstop GC cycles. The following example shows how to set the initiating heap occupancy to 75%:
Sets a target for the maximum GC pause time (in milliseconds). This is a soft goal, and the JVM will make its best effort to achieve it. By default, there is no maximum pause time value.
The following example shows how to set the maximum target pause time to 500 ms:
Sets the maximum size (in byes) of the memory allocation pool. This value must be a multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is chosen at runtime based on system configuration. For server deployments, - XX:InitialHeapSize and - XX:MaxHeapSize are often set to the same value. See the section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection Tuning Guide at docs. oracle/javase/8/docs/technotes/guides/vm/gctuning/index. html .
The following examples show how to set the maximum allowed size of allocated memory to 80 MB using various units:
The - XX:MaxHeapSize option is equivalent to - Xmx .
Sets the maximum allowed percentage of free heap space (0 to 100) after a GC event. If free heap space expands above this value, then the heap will be shrunk. By default, this value is set to 70%.
The following example shows how to set the maximum free heap ratio to 75%:
Sets the maximum amount of native memory that can be allocated for class metadata. By default, the size is not limited. The amount of metadata for an application depends on the application itself, other running applications, and the amount of memory available on the system.
The following example shows how to set the maximum class metadata size to 256 MB:
Sets the maximum size (in bytes) of the heap for the young generation (nursery). The default value is set ergonomically.
Sets the maximum tenuring threshold for use in adaptive GC sizing. The largest value is 15. The default value is 15 for the parallel (throughput) collector, and 6 for the CMS collector.
The following example shows how to set the maximum tenuring threshold to 10:
Sets the size of the allocated class metadata space that will trigger a garbage collection the first time it is exceeded. This threshold for a garbage collection is increased or decreased depending on the amount of metadata used. The default size depends on the platform.
Sets the minimum allowed percentage of free heap space (0 to 100) after a GC event. If free heap space falls below this value, then the heap will be expanded. By default, this value is set to 40%.
The following example shows how to set the minimum free heap ratio to 25%:
Sets the ratio between young and old generation sizes. By default, this option is set to 2. The following example shows how to set the young/old ratio to 1:
Sets the initial size (in bytes) of the heap for the young generation (nursery). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
The young generation region of the heap is used for new objects. GC is performed in this region more often than in other regions. If the size for the young generation is too low, then a large number of minor GCs will be performed. If the size is too high, then only full GCs will be performed, which can take a long time to complete. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size.
The following examples show how to set the initial size of young generation to 256 MB using various units:
The - XX:NewSize option is equivalent to - Xmn .
Sets the number of threads used for parallel garbage collection in the young and old generations. The default value depends on the number of CPUs available to the JVM.
For example, to set the number of threads for parallel GC to 2, specify the following option:
Enables parallel reference processing. By default, this option is disabled.
Enables printing of information about adaptive generation sizing. By default, this option is disabled.
Enables printing of messages at every GC. By default, this option is disabled.
Enables printing of how much time elapsed since the last pause (for example, a GC pause). By default, this option is disabled.
Enables printing of how much time the pause (for example, a GC pause) lasted. By default, this option is disabled.
Enables printing of a date stamp at every GC. By default, this option is disabled.
Enables printing of detailed messages at every GC. By default, this option is disabled.
Enables printing of time stamps for every individual GC worker thread task. By default, this option is disabled.
Enables printing of time stamps at every GC. By default, this option is disabled.
Prints detailed deduplication statistics. By default, this option is disabled. See the - XX:+UseStringDeduplication option.
Enables printing of tenuring age information. The following is an example of the output:
Age 1 objects are the youngest survivors (they were created after the previous scavenge, survived the latest scavenge, and moved from eden to survivor space). Age 2 objects have survived two scavenges (during the second scavenge they were copied from one survivor space to the next). E assim por diante.
In the preceding example, 28 992 024 bytes survived one scavenge and were copied from eden to survivor space, 1 366 864 bytes are occupied by age 2 objects, etc. The third value in each row is the cumulative size of objects of age n or less.
By default, this option is disabled.
Enables GC of the young generation before each full GC. This option is enabled by default. Oracle recommends that you do not disable it, because scavenging the young generation before a full GC can reduce the number of objects reachable from the old generation space into the young generation space. To disable GC of the young generation before each full GC, specify - XX:-ScavengeBeforeFullGC .
Sets the amount of time (in milliseconds) a softly reachable object is kept active on the heap after the last time it was referenced. The default value is one second of lifetime per free megabyte in the heap. The - XX:SoftRefLRUPolicyMSPerMB option accepts integer values representing milliseconds per one megabyte of the current heap size (for Java HotSpot Client VM) or the maximum possible heap size (for Java HotSpot Server VM). This difference means that the Client VM tends to flush soft references rather than grow the heap, whereas the Server VM tends to grow the heap rather than flush soft references. In the latter case, the value of the - Xmx option has a significant effect on how quickly soft references are garbage collected.
The following example shows how to set the value to 2.5 seconds:
String objects reaching the specified age are considered candidates for deduplication. An object's age is a measure of how many times it has survived garbage collection. This is sometimes referred to as tenuring; see the - XX:+PrintTenuringDistribution option. Note that String objects that are promoted to an old heap region before this age has been reached are always considered candidates for deduplication. The default value for this option is 3 . See the - XX:+UseStringDeduplication option.
Sets the ratio between eden space size and survivor space size. By default, this option is set to 8. The following example shows how to set the eden/survivor space ratio to 4:
Sets the desired percentage of survivor space (0 to 100) used after young garbage collection. By default, this option is set to 50%.
The following example shows how to set the target survivor space ratio to 30%:
Sets the initial size (in bytes) of a thread-local allocation buffer (TLAB). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. If this option is set to 0, then the JVM chooses the initial size automatically.
The following example shows how to set the initial TLAB size to 512 KB:
Enables the use of adaptive generation sizing. This option is enabled by default. To disable adaptive generation sizing, specify - XX:-UseAdaptiveSizePolicy and set the size of the memory allocation pool explicitly (see the - XX:SurvivorRatio option).
Enables the use of the occupancy value as the only criterion for initiating the CMS collector. By default, this option is disabled and other criteria may be used.
Enables the use of the CMS garbage collector for the old generation. Oracle recommends that you use the CMS garbage collector when application latency requirements cannot be met by the throughput ( - XX:+UseParallelGC ) garbage collector. The G1 garbage collector ( - XX:+UseG1GC ) is another alternative.
By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM. When this option is enabled, the - XX:+UseParNewGC option is automatically set and you should not disable it, because the following combination of options has been deprecated in JDK 8: - XX:+UseConcMarkSweepGC - XX:-UseParNewGC .
Enables the use of the garbage-first (G1) garbage collector. It is a server-style garbage collector, targeted for multiprocessor machines with a large amount of RAM. It meets GC pause time goals with high probability, while maintaining good throughput. The G1 collector is recommended for applications requiring large heaps (sizes of around 6 GB or larger) with limited GC latency requirements (stable and predictable pause time below 0.5 seconds).
By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM.
Enables the use of a policy that limits the proportion of time spent by the JVM on GC before an OutOfMemoryError exception is thrown. This option is enabled, by default and the parallel GC will throw an OutOfMemoryError if more than 98% of the total time is spent on garbage collection and less than 2% of the heap is recovered. When the heap is small, this feature can be used to prevent applications from running for long periods of time with little or no progress. To disable this option, specify - XX:-UseGCOverheadLimit .
Enables performance optimization of an application on a machine with nonuniform memory architecture (NUMA) by increasing the application's use of lower latency memory. By default, this option is disabled and no optimization for NUMA is made. The option is only available when the parallel garbage collector is used ( - XX:+UseParallelGC ).
Enables the use of the parallel scavenge garbage collector (also known as the throughput collector) to improve the performance of your application by leveraging multiple processors.
By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM. If it is enabled, then the - XX:+UseParallelOldGC option is automatically enabled, unless you explicitly disable it.
Enables the use of the parallel garbage collector for full GCs. By default, this option is disabled. Enabling it automatically enables the - XX:+UseParallelGC option.
Enables the use of parallel threads for collection in the young generation. By default, this option is disabled. It is automatically enabled when you set the - XX:+UseConcMarkSweepGC option. Using the - XX:+UseParNewGC option without the - XX:+UseConcMarkSweepGC option was deprecated in JDK 8.
Enables the use of the serial garbage collector. This is generally the best choice for small and simple applications that do not require any special functionality from garbage collection. By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM.
Enables string deduplication. By default, this option is disabled. To use this option, you must enable the garbage-first (G1) garbage collector. See the - XX:+UseG1GC option.
String deduplication reduces the memory footprint of String objects on the Java heap by taking advantage of the fact that many String objects are identical. Instead of each String object pointing to its own character array, identical String objects can point to and share the same character array.
Enables the use of thread-local allocation blocks (TLABs) in the young generation space. This option is enabled by default. To disable the use of TLABs, specify - XX:-UseTLAB .
Deprecated and Removed Options.
These options were included in the previous release, but have since been considered unnecessary.
Enables incremental garbage collection. This option was deprecated in JDK 8 with no replacement.
Loads the specified debugging/profiling library. This option was superseded by the - agentlib option.
Sets the percentage of time (0 to 100) between minor collections that the concurrent collector is allowed to run. This option was deprecated in JDK 8 with no replacement, following the deprecation of the - XX:+CMSIncrementalMode option.
Sets the percentage of time (0 to 100) between minor collections that is the lower bound for the duty cycle when - XX:+CMSIncrementalPacing is enabled. This option was deprecated in JDK 8 with no replacement, following the deprecation of the - XX:+CMSIncrementalMode option.
Enables the incremental mode for the CMS collector. This option was deprecated in JDK 8 with no replacement, along with other options that start with CMSIncremental .
Sets the percentage of time (0 to 100) by which the incremental mode duty cycle is shifted to the right within the period between minor collections. This option was deprecated in JDK 8 with no replacement, following the deprecation of the - XX:+CMSIncrementalMode option.
Enables automatic adjustment of the incremental mode duty cycle based on statistics collected while the JVM is running. This option was deprecated in JDK 8 with no replacement, following the deprecation of the - XX:+CMSIncrementalMode option.
Sets the percentage of time (0 to 100) used to add conservatism when computing the duty cycle. This option was deprecated in JDK 8 with no replacement, following the deprecation of the - XX:+CMSIncrementalMode option.
Sets the percentage of the permanent generation occupancy (0 to 100) at which to start a GC. This option was deprecated in JDK 8 with no replacement.
Sets the maximum permanent generation space size (in bytes). This option was deprecated in JDK 8, and superseded by the - XX:MaxMetaspaceSize option.
Sets the space (in bytes) allocated to the permanent generation that triggers a garbage collection if it is exceeded. This option was deprecated un JDK 8, and superseded by the - XX:MetaspaceSize option.
Enables splitting of the verification process. By default, this option was enabled in the previous releases, and verification was split into two phases: type referencing (performed by the compiler) and type checking (performed by the JVM runtime). This option was deprecated in JDK 8, and verification is now split by default without a way to disable it.
Enables caching of commonly allocated strings. This option was removed from JDK 8 with no replacement.
Performance Tuning Examples.
The following examples show how to use experimental tuning flags to either optimize throughput or to provide lower response time.
Example 1 - Tuning for Higher Throughput Example 2 - Tuning for Lower Response Time.
Large Pages.
Also known as huge pages, large pages are memory pages that are significantly larger than the standard memory page size (which varies depending on the processor and operating system). Large pages optimize processor Translation-Lookaside Buffers.
A Translation-Lookaside Buffer (TLB) is a page translation cache that holds the most-recently used virtual-to-physical address translations. TLB is a scarce system resource. A TLB miss can be costly as the processor must then read from the hierarchical page table, which may require multiple memory accesses. By using a larger memory page size, a single TLB entry can represent a larger memory range. There will be less pressure on TLB, and memory-intensive applications may have better performance.
However, large pages page memory can negatively affect system performance. For example, when a large mount of memory is pinned by an application, it may create a shortage of regular memory and cause excessive paging in other applications and slow down the entire system. Also, a system that has been up for a long time could produce excessive fragmentation, which could make it impossible to reserve enough large page memory. When this happens, either the OS or JVM reverts to using regular pages.
Large Pages Support.
Only Windows Server 2003 supports large pages. To use this feature, the administrator must first assign additional privilege to the user who will be running the application:
Select Control Panel -> Administrative Tools -> Local Security Policy .
Select Local Policies -> User Rights Assignment .
Double click Lock pages in memory ; add users and/or groups.
Reboot your system.
Note that these steps are required even if it is the administrator who will be running the application, as administrators by default do not have the privilege to lock pages in memory.
Application Class Data Sharing.
Application Class Data Sharing (AppCDS) extends CDS (see docs. oracle/javase/8/docs/technotes/guides/vm/class-data-sharing. html ) to enable classes from the standard extensions directories (specified by the system property java. ext. dirs ; see docs. oracle/javase/8/docs/technotes/guides/extensions/spec. html ) and the application class path (see "Setting the Class Path") to be placed in the shared archive. AppCDS reduces the footprint and decreases start-up time of your applications provided that a substantial number of classes are loaded from the application class path.
This is a commercial feature that requires you to also specify the - XX:+UnlockCommercialFeatures option. This is also an experimental feature; it may change in future releases.
Creating a Shared Archive File, and Running an Application with It.
The following steps create a shared archive file that contains all the classes used by the test. Hello application. The last step runs the application with the shared archive file.
Create a list of all classes used by the test. Hello application. The following command creates a file named hello. classlist that contains a list of all classes used by this application:
java - Xshare:off - XX:+UnlockCommercialFeatures - XX:DumpLoadedClassList=hello. classlist - XX:+UseAppCDS - cp hello. jar test. Hello.
Note that the - cp parameter must contain only JAR files; the - XX:+UseAppCDS option does not support class paths that contain directory names.
Create a shared archive, named hello. jsa , that contains all the classes in hello. classlist :
java - XX:+UnlockCommercialFeatures - Xshare:dump - XX:+UseAppCDS - XX:SharedArchiveFile=hello. jsa - XX:SharedClassListFile=hello. classlist - cp hello. jar.
Note that the - cp parameter used at archive creation time must be the same as (or a prefix of) the - cp used at run time.
Run the application test. Hello with the shared archive hello. jsa :
java - XX:+UnlockCommercialFeatures - Xshare:on - XX:+UseAppCDS - XX:SharedArchiveFile=hello. jsa - cp hello. jar test. Hello.
Ensure that you have specified the option - Xshare:on or - Xshare:auto .
Verify that the test. Hello application is using the class contained in the hello. jsa shared archive:
java - XX:+UnlockCommercialFeatures - Xshare:on - XX:+UseAppCDS - XX:SharedArchiveFile=hello. jsa - cp hello. jar - verbose:class test. Hello.
The output of this command should contain the following text:
Loaded test. Hello from shared objects file by sun/misc/Launcher$AppClassLoader.
Sharing a Shared Archive across Multiple Application Processes.
You can share the same archive file across multiple applications processes that have the exact same class path or share a common class path prefix. This reduces memory usage as the archive is memory-mapped into the address space of the processes. The operating system automatically shares the read-only pages across these processes.
The following steps create a shared archive that both applications Hello and Hi can use.
Create a list of all classes used by the Hello application and another list for the Hi application:
java - XX:+UnlockCommercialFeatures - XX:DumpLoadedClassList=hello. classlist - XX:+UseAppCDS - cp common. jar:hello. jar Hello.
java - XX:+UnlockCommercialFeatures - XX:DumpLoadedClassList=hi. classlist - XX:+UseAppCDS - cp common. jar:hi. jar Hi.
Note that because the Hello and Hi applications share a common class path prefix (both of their class paths start with common. jar ), these two applications can share a shared archive file.
Create a single list of classes used by all the applications that will share the shared archive file.
The following commands combine the files hello. classlist and hi. classlist to one file, common. classlist :
type hello. classlist hi. classlist > common. classlist.
Create a shared archive, named common. jsa , that contains all the classes in common. classlist :
java - XX:+UnlockCommercialFeatures - Xshare:dump - XX:SharedArchiveFile=common. jsa - XX:+UseAppCDS - XX:SharedClassListFile=common. classlist - cp common. jar.
The value of the - cp parameter is the common class path prefix shared by the Hello and Hi applications.
Run the Hello and Hi applications with the same shared archive:

Javafx vm options

It is possible to pass command line options to the Java Virtual Machine (JVM). These options can change certain things about how Java runs, such as the maximum heap size, or whether antialiasing is used in certain places.
For operating systems such as Linux where jEdit is started via a shell script, you can easily edit the jedit script and place JVM arguments in the correct place. If you are using the - jar command line option with the java command to run jEdit (which is how the default shell scripts do it), remember that the - jar parameter must be the last java option, followed immediately by the path to jedit. jar and then any jEdit command line options.
On a Windows install that uses jEdit. exe , the JVM options are located in a separate file, called jEdit. l4j. ini . Create or edit this file in the same directory as jEdit. exe and place one JVM option per line.
On Mac OS X, the jEdit. app bundle gets JVM options from a file called Contents/Info. plist , which can be edited with a text editor.
There is no complete list of options to java , since it can vary from one platform to another. Some of can be found by typing the commands java -? or man java . Common JVM options that are used with jEdit and work on all platforms are: