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[DOCS] Remove PrintCompressedOopsMode JVM option (#73741) (#73954)
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Changes:
* Removes a reference to the
  `-XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode` JVM option. This
  option is no longer supported.
* Combines `Xms/Xmx` recommendations for compressed oops.

Closes #71644.

Co-authored-by: Rick Boyd <boyd.richardj@gmail.com>
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jrodewig and DJRickyB authored Jun 9, 2021
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Showing 1 changed file with 4 additions and 23 deletions.
27 changes: 4 additions & 23 deletions docs/reference/setup/advanced-configuration.asciidoc
Original file line number Diff line number Diff line change
Expand Up @@ -110,35 +110,16 @@ NOTE: When running in a container, such as <<docker,Docker>>, total memory is
defined as the amount of memory visible to the container, not the total system
memory on the host.

* Set `Xms` and `Xmx` to no more than 32 GB, the approximate threshold for
compressed ordinary object pointers (oops). To verify you are under the
threshold, check `elasticsearch.logs` for an entry like this:
* Set `Xms` and `Xmx` to no more than the threshold for compressed ordinary
object pointers (oops). The exact threshold varies but 26GB is safe on most
systems and can be as large as 30GB on some systems. To verify you are under the
threshold, check the {es} log for an entry like this:
+
[source,txt]
----
heap size [1.9gb], compressed ordinary object pointers [true]
----

* Set `Xms` and `Xmx` 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 {es} with the JVM options
`-XX:+UnlockDiagnosticVMOptions -XX:+PrintCompressedOopsMode` and checking
`elasticsearch.logs` for an entry like this:
+
[source,txt]
----
heap address: 0x000000011be00000, size: 27648 MB, zero based Compressed Oops
----
+
This entry shows that zero-based compressed oops are enabled. If zero-based
compressed oops are not enabled, the entry looks like this:
+
[source,txt]
----
heap address: 0x0000000118400000, size: 28672 MB, Compressed Oops with base: 0x00000001183ff000
----

The more heap available to {es}, 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
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