This commit introduces the ability to override JVM options by adding
custom JVM options files to a jvm.options.d directory. This simplifies
administration of Elasticsearch by not requiring administrators to keep
the root jvm.options file in sync with changes that we make to the root
jvm.options file. Instead, they are not expected to modify this file but
instead supply their own in jvm.options.d. In Docker installations, this
means they can bind mount this directory in. In future versions of
Elasticsearch, we can consider removing the root jvm.options file
(instead, providing all options there as system JVM options).
This commit slightly reworks the recommendations in the docs about setting the
heap size:
* the "rules of thumb" are actually instructions that should be followed
* the reason for setting `Xmx` to 50% of the heap size is more subtle than just
leaving space for the filesystem cache
* it is normal to see Elasticsearch using more memory than `Xmx`
* replace `cutoff` and `limit` with `threshold` since all three terms are used
interchangeably
* since we recommend setting `Xmx` equal to `Xms`, avoid talking about setting
`Xmx` in isolation
Relates #41954
This commit reorganizes some of the content in the configuring
Elasticsearch section of the docs. The changes are:
- move JVM options out of system configuration into configuring
Elasticsearch
- move JVM options to its own page of the docs
- move configuring the heap to important Elasticsearch settings
- move configuring the heap to its own page of the docs
- move all important settings to individual pages in the docs
- remove bootstrap.memory_lock from important settings, this is covered
in the swap section of system configuration
Relates #27755
Jason Tedor
David Turner