add warning about inaccurate/confusing memory usage in hardware dashboard

[RichardJCai]

Richard Cai (RichardJCai) commented:

https://www.cockroachlabs.com/docs/v20.2/ui-hardware-dashboard#memory-usage

The memory usage in the ui hardware dashboard can be inaccurate due to go's memory tracking.
Prior to go 1.16, memory will be reported as used until it is actually reclaimed by the operating system. This leads to some confusing UX when memory isn't actually used by CRDB but the dashboard will report it as used.

This will be fixed in go 1.16 however it may be worth nothing this until we upgrade to go 1.16. Currently, CockroachDB versions 21.1 and earlier are affected.

I ran into this UX issue when testing user connections, creating ~30000 user connections increased the memory to 2gb but killing the connections did not result in the memory usage decreasing in the dashboard.

Relevant go issue, which we can link to from the docs:
golang/go#42330

Jira Issue: DOC-1069

[exalate-issue-sync]

Andrew Feierabend (andf-crl) commented:
This memory reporting issue was fixed in go {{1.16}}, which indeed has been the version of {{go}} behind CRDB since v21.2. No updates to currently-documented docs versions necessary; closing as a docs no-op.