[2pt] Consider to recommend disabling swap / overcommit

[Totktonada]

Recommend disabling certain system settings for memtx

Product: Tarantool Audience/target: dev Root document: https://www.tarantool.io/en/doc/latest/book/box/engines/memtx/#summary ? TBD SME: @ Mons, @ Totktonada

Details

There is a gap in the docs. All of the following hasn't been documented yet:

• It is best to disable the overcommit Linux kernel setting when using memtx. Overcommit leads to a runtime error. Overcommit documentation: see the sections on overcommit_kbytes, overcommit_memory, overcommit_ratio.
• Using the swap mechanism may lead to lagging in some scenarios.
• Swap + overcommit = huge lags.

@ Mons can provide information on how this works in practice, @ Totktonada knows well how it works in theory.

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Original message from @ Totktonada:

Regarding swap: I guess fast fail (OOM killer) is much more wishful in the general case comparing to dramatically degraded performance (near to the level of full service unavailability).

Regarding sysctl vm.overcommit_memory: it is better to say that memtx_memory is incorrect on starting rather than be hit by the physical memory limit during work.

I guess @Mons can share experience of projects-in-production.

[Totktonada]

What kind of feedback is needed and from who?