IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Advanced configuration settings

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Advanced configuration settings

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The settings below are considered advanced and for expert users only. In most cases the Elasticsearch-provided default settings should be used. Take caution when modifying these settings as this could result in undesired behavior or reduced system performance.

Setting JVM heap size

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If you need to override the default heap size settings, follow the best practices below.

Elasticsearch assigns the entire heap specified in jvm.options via the Xms (minimum heap size) and Xmx (maximum heap size) settings. These two settings must 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 total system memory. 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]
```
Set Xmx and Xms to no more than the threshold for zero-based compressed oops. The exact threshold varies but 26GB is safe on most systems and can be as large as 30GB 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
```
This line shows that zero-based compressed oops are enabled. If zero-based compressed oops are not enabled, you’ll 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. This leaves less memory for the operating system to use for the filesystem cache. Larger heaps can also cause longer garbage collection pauses.

Here is an example of how to set the heap size via a jvm.options.d/ file:

-Xms2g 
-Xmx2g

	Set the minimum heap size to 2g.
	Set the maximum heap size to 2g.

In production, we recommend using jvm.options.d to configure heap sizes.

For testing, you can also set the heap sizes using the ES_JAVA_OPTS environment variable. The ES_JAVA_OPTS variable overrides all other JVM options. We do not recommend using ES_JAVA_OPTS in production.

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. See Installing Elasticsearch as a Service on Windows.

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