Add warnings for potential ergonomics failures for JDK8/Windows #48968
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…ue) (elastic#48365) Our JVM ergonomics extract max heap size from JDK PrintFlagsFinal output. On JDK 8, there is a system-dependent bug where memory sizes are cast to 32-bit integers. On affected systems (namely, Windows), when 1/4 of physical memory is more than the maximum integer value, the output of PrintFlagsFinal will be inaccurate. In the pathological case, where the max heap size would be a multiple of 4g, the test will fail. The practical effect of this bug, beyond test failures, is that we may set MaxDirectMemorySize to an incorrect value on Windows. This commit adds a warning about this situation during startup.
…8657) * Always pass user-specified MaxDirectMemorySize We had been testing whether a user had passed a value for MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal -version". If MaxDirectMemorySize equals zero, we set it to half of max heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly truncates values over 4g and returns multiples of 4g as zero. In order to always respect the user-defined settings, we need to check our input to see if an "-XX:MaxDirectMemorySize" value has been passed. * Always warn for Windows/jdk8 ergo issue Even if a user has set MaxDirectMemorySize, they aren't future-proof for this JDK bug. With this change, we issue a general warning for the windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is unset.
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Pinging @elastic/es-core-infra (:Core/Infra/Core) |
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Our JVM ergonomics extract max heap size from JDK PrintFlagsFinal output. On JDK 8, there is a system-dependent bug where memory sizes are cast to 32-bit integers. On affected systems (namely, Windows), when 1/4 of physical memory is more than the maximum integer value, the output of PrintFlagsFinal will be inaccurate. In the pathological case, where the max heap size would be a multiple of 4g, the test will fail.
The practical effect of this bug, beyond test failures, is that we may set MaxDirectMemorySize to an incorrect value on Windows. This commit adds a warning about this situation during startup.
Additionally, we had been testing whether a user had passed a value for MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal -version". If MaxDirectMemorySize equals zero, we set it to half of max heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly truncates values over 4g and returns multiples of 4g as zero. In order to always respect the user-defined settings, we need to check our input to see if an "-XX:MaxDirectMemorySize" value has been passed.
Finally, even if a user has set MaxDirectMemorySize, they aren't future-proof for this JDK bug. With this change, we issue a general warning for the windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is unset.