PR #97666 - cli,server: set GOMEMLIMIT by default (1 of 2)

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#97666
Commit: cockroachdb/cockroach@2e6ae80
Fixes: cockroachdb/cockroach#95690

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Release note (cli change): New flag --max-go-memory is introduced to
start command. It controls the soft memory limit on the Go runtime
which adjusts the behavior of the Go garbage collector to try keeping the
memory usage under the soft memory limit (the limit is "soft" in a sense
that it is not enforced if live objects (RSS) exceed it). Similar to the
--max-sql-memory flag, the new flag --max-go-memory accepts numbers
interpreted as bytes, size suffixes (e.g. 1GB and 1GiB) or a percentage
of physical memory (e.g. .25). If left unspecified, the flag defaults to
2.25x of --max-sql-memory (subject to --max-go-memory + 1.15x --cache
not exceeding 90% of available RAM). Set to 0 to disable the soft memory
limit (not recommended). If GOMEMLIMIT env var is set and
--max-go-memory is not, then the value from the env var is used; if
both are set, then the flag takes precedence.

Here is a few examples of how the default value is calculated on
a machine with 16GiB of RAM:

Command line flags	Computed max SQL memory	Computed cache size	Computed max Go memory
--max-sql-memory=.25 --cache=.25	4GiB	4GiB	9GiB
--max-sql-memory=.1 --cache=.5	1.6GiB	8GiB	3.6GiB
--max-sql-memory=.25 --cache=.4	4GiB	6.4GiB	7.04GiB
--max-sql-memory=100MiB	100MiB	128MiB	256MiB
--max-sql-memory=.4 --cache=.2 --max-go-memory=100MiB	6.4GiB	3.2GiB	100MiB

Explanation:

• in the first two lines we just use the default formula 2.25x --max-sql-memory
• in the third line, the default formula results in exceeding the upper
  bound on total usage (including the cache), so we use the upper bound
  determined as 0.9 * total RAM - 1.15 * cache size
• in the fourth line, the default formula results in 225MiB which is
  smaller than the lower bound of 256MiB, so we bump the value to that
  lower bound
• in the fifth line, we use the value specified by the user (even though
  it is smaller than the lower bound on the default value).

Jira Issue: DOC-7165