-XX:MaxRAMFraction = 1对于在容器环境中进行生产是否安全? [英] Is -XX:MaxRAMFraction=1 safe for production in a containered environment?

问题描述

Java 8/9带来了对-XX:+UseCGroupMemoryLimitForHeap(带有-XX:+UnlockExperimentalVMOptions)的支持.这会将-XX:MaxRAM设置为cgroup内存限制.默认情况下，JVM分配大约25％的最大RAM，因为-XX:MaxRAMFraction默认为4.

Java 8/9 brought support for -XX:+UseCGroupMemoryLimitForHeap (with -XX:+UnlockExperimentalVMOptions). This sets -XX:MaxRAM to the cgroup memory limit. Per default, the JVM allocates roughly 25% of the max RAM, because -XX:MaxRAMFraction defaults to 4.

示例:

MaxRAM = 1g
MaxRAMFraction = 4
JVM is allowed to allocate: MaxRAM / MaxRAMFraction = 1g / 4 = 256m

仅使用25％的配额对于部署(通常)由单个JVM进程组成的部署来说似乎是浪费.因此，现在人们设置了-XX:MaxRAMFraction=1，因此理论上允许JVM使用100％的MaxRAM.

Using only 25% of the quota seems like waste for a deployment which (usually) consists of a single JVM process. So now people set -XX:MaxRAMFraction=1, so the JVM is theoretically allowed to use 100% of the MaxRAM.

对于1g的示例，这通常导致堆大小约为900m.这似乎有点高-JVM或其他东西(如远程Shell或进程外任务)没有太多可用空间.

For the 1g example, this often results in heap sizes around 900m. This seems a bit high - there is not a lot of free room for the JVM or other stuff like remote shells or out-of-process tasks.

那么该配置(-XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=1)对于产品甚至最佳实践是否被认为是安全的?还是我还是应该手动选择-Xmx，-Xms，-Xss等?

So is this configuration (-XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=1) considered safe for prod or even best practice? Or should I still hand pick -Xmx, -Xms, -Xss and so on?

推荐答案

我们进行了一些简单的测试，结果表明，设置-XX:MaxRAM=$QUOTA和-XX:MaxRAMFraction=1会导致装入的容器被杀死. JVM分配了超过900M的堆，这太多了. -XX:MaxRAMFraction=2似乎很安全.

We did some simple testing which showed that setting -XX:MaxRAM=$QUOTA and -XX:MaxRAMFraction=1 results in killed containers under load. The JVM allocates more than 900M heap, which is way too much. -XX:MaxRAMFraction=2 seems safe(ish).

请记住，您可能希望为其他进程留出空间，例如在容器中获取调试shell(docker exec)或诊断程序.

Keep in mind that you may want to leave headroom for other processes like getting a debug shell (docker exec) or diagnostics in the container.

我们已在文章.货币报价:

TL'DR: Java内存管理和配置仍然很复杂.自Java 9/8u131起，尽管JVM可以读取cgroup内存限制并相应地调整内存使用量，但这并不是万灵药.您需要知道-XX:+UseCGroupMemoryLimitForHeap的作用，并且需要为每个部署微调一些参数.否则，您可能会在最坏的时间浪费资源和金钱，或者杀死集装箱. -XX:MaxRAMFraction=1特别危险. Java 10+带来了许多改进，但仍需要手动配置.为了安全起见，请对您的东西进行负载测试.

TL'DR: Java memory management and configuration is still complex. Although the JVM can read cgroup memory limits and adapt memory usage accordingly since Java 9/8u131, it’s not a golden bullet. You need to know what -XX:+UseCGroupMemoryLimitForHeap does and you need to fine tune some parameters for every deployment. Otherwise you risk wasting resources and money or getting your containers killed at the worst time possible. -XX:MaxRAMFraction=1 is especially dangerous. Java 10+ brings a lot of improvements but still needs manual configuration. To be safe, load test your stuff.

和

最优雅的解决方案是升级到Java 10+. Java 10弃用了-XX:+UseCGroupMemoryLimitForHeap(11)并引入了-XX:+UseContainerSupport(12)，它将取代它.它还引入了-XX:MaxRAMPercentage(13)，其值在0到100之间.这允许对允许JVM分配的RAM数量进行精细控制.由于默认情况下启用了+UseContainerSupport，因此所有操作均应立即可用.

The most elegant solution is to upgrade to Java 10+. Java 10 deprecates -XX:+UseCGroupMemoryLimitForHeap (11) and introduces -XX:+UseContainerSupport (12), which supersedes it. It also introduces -XX:MaxRAMPercentage (13) which takes a value between 0 and 100. This allows fine grained control of the amount of RAM the JVM is allowed to allocate. Since +UseContainerSupport is enabled by default, everything should work out of the box.

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我们已经写了一些关于-XX:+UseContainerSupport

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Edit #2: we've written a little bit more about -XX:+UseContainerSupport

Java 10引入了+UseContainerSupport(默认情况下启用)，它使JVM在容器环境中使用合理的默认值.自8u191以来，此功能已反向移植到Java 8，这可能允许大量野生Java部署正确配置其内存.

Java 10 introduced +UseContainerSupport (enabled by default) which makes the JVM use sane defaults in a container environment. This feature is backported to Java 8 since 8u191, potentially allowing a huge percentage of Java deployments in the wild to properly configure their memory.

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