diff --git a/docs/reference/setup/important-settings/heap-size.asciidoc b/docs/reference/setup/important-settings/heap-size.asciidoc index 77aa23b61df..890a9786e09 100644 --- a/docs/reference/setup/important-settings/heap-size.asciidoc +++ b/docs/reference/setup/important-settings/heap-size.asciidoc @@ -7,42 +7,48 @@ to ensure that Elasticsearch has enough heap available. Elasticsearch will assign the entire heap specified in <> via the `Xms` (minimum heap size) and `Xmx` (maximum -heap size) settings. +heap size) settings. You should set these two settings to be equal to each +other. The value for these setting depends on the amount of RAM available on your -server. Good rules of thumb are: +server: -* Set the minimum heap size (`Xms`) and maximum heap size (`Xmx`) to be equal to - each other. +* Set `Xmx` and `Xms` to no more than 50% of your physical RAM. {es} requires + memory for purposes other than the JVM heap and it is important to leave + space for this. For instance, {es} uses off-heap buffers for efficient + network communication, relies on the operating system's filesystem cache for + efficient access to files, and the JVM itself requires some memory too. It is + normal to observe the {es} process using more memory than the limit + configured with the `Xmx` setting. -* The more heap available to Elasticsearch, the more memory it can use for - caching. But note that too much heap can subject you to long garbage - collection pauses. - -* Set `Xmx` to no more than 50% of your physical RAM, to ensure that there is - enough physical RAM left for kernel file system caches. - -* Don’t set `Xmx` to above the cutoff that the JVM uses for compressed object - pointers (compressed oops); the exact cutoff varies but is near 32 GB. You can - verify that you are under the limit by looking for a line in the logs like the - following: +* Set `Xmx` and `Xms` to no more than the threshold that the JVM uses for + compressed object pointers (compressed oops); the exact threshold varies but + is near 32 GB. You can verify that you are under the threshold by looking for a + line in the logs like the following: + heap size [1.9gb], compressed ordinary object pointers [true] -* Even better, try to stay below the threshold for zero-based compressed oops; - the exact cutoff varies but 26 GB is safe on most systems, but can be as large - as 30 GB on some systems. You can verify that you are under the limit by - starting Elasticsearch with the JVM options `-XX:+UnlockDiagnosticVMOptions - -XX:+PrintCompressedOopsMode` and looking for a line like the following: +* Ideally set `Xmx` and `Xms` to no more than the threshold for zero-based + compressed oops; the exact threshold varies but 26 GB is safe on most + systems, but can be as large as 30 GB on some systems. You can verify that + you are under this threshold by starting {es} with the JVM options + `-XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode` and looking for + a line like the following: + -- heap address: 0x000000011be00000, size: 27648 MB, zero based Compressed Oops -showing that zero-based compressed oops are enabled instead of +showing that zero-based compressed oops are enabled. If zero-based compressed +oops are not enabled then you will see a line like the following instead: heap address: 0x0000000118400000, size: 28672 MB, Compressed Oops with base: 0x00000001183ff000 -- +The more heap available to {es}, the more memory it can use for its internal +caches, but the less memory it leaves available for the operating system to use +for the filesystem cache. Also, larger heaps can cause longer garbage +collection pauses. + Here are examples of how to set the heap size via the jvm.options file: [source,txt] @@ -66,7 +72,7 @@ ES_JAVA_OPTS="-Xms4000m -Xmx4000m" ./bin/elasticsearch <2> <2> Set the minimum and maximum heap size to 4000 MB. NOTE: Configuring the heap for the <> is -different than the above. The values initially populated for the Windows service -can be configured as above but are different after the service has been +different than the above. The values initially populated for the Windows +service can be configured as above but are different after the service has been installed. Consult the <> for additional details.