105 lines
3.7 KiB
Plaintext
105 lines
3.7 KiB
Plaintext
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[[setup-configuration-memory]]
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=== Disable swapping
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Most operating systems try to use as much memory as possible for file system
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caches and eagerly swap out unused application memory. This can result in
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parts of the JVM heap being swapped out to disk.
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Swapping is very bad for performance and for node stability and should be
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avoided at all costs. It can cause garbage collections to last for **minutes**
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instead of milliseconds and can cause nodes to respond slowly or even to
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disconnect from the cluster.
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There are three approaches to disabling swapping:
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[[mlockall]]
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==== Enable `bootstrap.mlockall`
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The first option is to use
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http://opengroup.org/onlinepubs/007908799/xsh/mlockall.html[mlockall] on Linux/Unix systems, or https://msdn.microsoft.com/en-us/library/windows/desktop/aa366895%28v=vs.85%29.aspx[VirtualLock] on Windows, to
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try to lock the process address space into RAM, preventing any Elasticsearch
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memory from being swapped out. This can be done, by adding this line
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to the `config/elasticsearch.yml` file:
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[source,yaml]
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--------------
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bootstrap.mlockall: true
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--------------
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WARNING: `mlockall` might cause the JVM or shell session to exit if it tries
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to allocate more memory than is available!
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After starting Elasticsearch, you can see whether this setting was applied
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successfully by checking the value of `mlockall` in the output from this
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request:
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[source,sh]
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--------------
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curl 'http://localhost:9200/_nodes?pretty&filter_path=**.mlockall'
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--------------
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If you see that `mlockall` is `false`, then it means that the `mlockall`
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request has failed. You will also see a line with more information in the
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logs with the words `Unable to lock JVM Memory`.
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The most probable reason, on Linux/Unix systems, is that the user running
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Elasticsearch doesn't have permission to lock memory. This can be granted as follows:
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`.zip` and `.tar.gz`::
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Set <<ulimit,`ulimit -l unlimited`>> as root before starting Elasticsearch,
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or set `memlock` to `unlimited` in
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<<limits.conf,`/etc/security/limits.conf`>>.
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RPM and Debian::
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Set `MAX_LOCKED_MEMORY` to `unlimited` in the
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<<sysconfig,system configuration file>> (or see below for systems using `systemd`).
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Systems using `systemd`::
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Set `LimitMEMLOCK` to `infinity` in the <<systemd,systemd configuration>>.
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Another possible reason why `mlockall` can fail is that the temporary directory
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(usually `/tmp`) is mounted with the `noexec` option. This can be solved by
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specifying a new temp directory, by starting Elasticsearch with:
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[source,sh]
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--------------
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./bin/elasticsearch -Djava.io.tmpdir=/path/to/temp/dir
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--------------
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or using the `ES_JAVA_OPTS` environment variable:
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[source,sh]
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--------------
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export ES_JAVA_OPTS="$ES_JAVA_OPTS -Djava.io.tmpdir=/path/to/temp/dir"
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./bin/elasticsearch
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--------------
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[[disable-swap-files]]
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==== Disable all swap files
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The second option is to completely disable swap. Usually Elasticsearch
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is the only service running on a box, and its memory usage is controlled
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by the `ES_HEAP_SIZE` environment variable. There should be no need
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to have swap enabled.
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On Linux systems, you can disable swap temporarily
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by running: `sudo swapoff -a`. To disable it permanently, you will need
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to edit the `/etc/fstab` file and comment out any lines that contain the
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word `swap`.
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On Windows, the equivalent can be achieved by disabling the paging file entirely
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via `System Properties → Advanced → Performance → Advanced → Virtual memory`.
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[[swappiness]]
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==== Configure `swappiness`
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The second option available on Linux systems is to ensure that the sysctl value
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`vm.swappiness` is set to `1`. This reduces the kernel's tendency to swap and
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should not lead to swapping under normal circumstances, while still allowing
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the whole system to swap in emergency conditions.
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