Elasticsearch Elasticsearch Memlock: Best Practices and Configuration

By Opster Team

Updated: Jan 28, 2024

| 2 min read


Elasticsearch memlock is an important setting that can help prevent memory-related issues and improve the overall performance of your Elasticsearch cluster. This article will discuss the significance of memlock, best practices, and how to configure it for optimal performance. If you want to learn about Elasticsearch bootstrap memory_lock is set to false, check out this guide.

Importance of Memlock in Elasticsearch

Memlock is a setting that allows Elasticsearch to lock its memory into RAM, preventing the operating system from swapping out the memory to disk. Swapping can cause significant performance degradation, as disk access is much slower than RAM access. By enabling memlock, you can ensure that the Elasticsearch process’s memory remains in RAM, leading to better performance and stability.

Best Practices for Memlock Configuration

1. Enable memlock for Elasticsearch: To prevent swapping, it is recommended to enable memlock for the Elasticsearch process. This can be done by setting the `bootstrap.memory_lock` parameter to `true` in the `elasticsearch.yml` configuration file.

bootstrap.memory_lock: true

2. Configure the operating system to allow memory locking: To allow Elasticsearch to lock its memory, you need to configure the operating system to grant the necessary permissions. For Linux systems, you can set the `memlock` limit in the `/etc/security/limits.conf` file. Add the following lines, replacing `USERNAME` with the user running Elasticsearch:

USERNAME soft memlock unlimited
USERNAME hard memlock unlimited

For systemd-based systems, you can set the `LimitMEMLOCK` parameter in the Elasticsearch service file, usually located at `/etc/systemd/system/elasticsearch.service`. Add the following line under the `[Service]` section:


After making these changes, restart the Elasticsearch service for the new settings to take effect.

3.  Set the JVM heap size appropriately: To make the most of memory locking, it is crucial to set the JVM heap size correctly. The general recommendation is to allocate 50% of the available system memory to the JVM heap, but not more than 30.5GB, leaving the rest for file system caching and other processes. You can set the heap size in the `jvm.options` file, usually located in the `config` directory of your Elasticsearch installation.


Replace `<size>` with the desired heap size, such as `16g` for 16 GB.

4. Monitor memory usage: Regularly monitor your Elasticsearch cluster’s memory usage to ensure that it is operating within the allocated limits and that there is no excessive swapping. Tools like Elasticsearch’s Cluster Stats API and Node Stats API can provide valuable insights into memory usage.


By following these best practices and properly configuring memlock, you can significantly improve the performance and stability of your Elasticsearch cluster.
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