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Elasticsearch Reference [7.6] » Set up Elasticsearch » Important Elasticsearch configuration » Setting the heap size
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Setting the heap sizeedit

By default, Elasticsearch tells the JVM to use a heap with a minimum and maximum size of 1 GB. When moving to production, it is important to configure heap size to ensure that Elasticsearch has enough heap available.

Elasticsearch will assign the entire heap specified in jvm.options via the Xms (minimum heap size) and Xmx (maximum heap size) settings. You should set these two settings to be equal to each other.

The value for these settings depends on the amount of RAM available on your server:

  • Set Xmx and Xms to no more than 50% of your physical RAM. Elasticsearch requires memory for purposes other than the JVM heap and it is important to leave space for this. For instance, Elasticsearch 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 Elasticsearch process using more memory than the limit configured with the Xmx setting.

  • 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]

  • 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 Elasticsearch 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. 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 Elasticsearch, 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:

-Xms2g 
-Xmx2g

Set the minimum heap size to 2g.

Set the maximum heap size to 2g.

It is also possible to set the heap size via an environment variable. This can be done by commenting out the Xms and Xmx settings in the jvm.options file and setting these values via ES_JAVA_OPTS:

ES_JAVA_OPTS="-Xms2g -Xmx2g" ./bin/elasticsearch 
ES_JAVA_OPTS="-Xms4000m -Xmx4000m" ./bin/elasticsearch

Set the minimum and maximum heap size to 2 GB.

Set the minimum and maximum heap size to 4000 MB.

Configuring the heap for the Windows service 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 installed. Consult the Windows service documentation for additional details.

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