release-23.1: sql: fix a couple of memory leaks around memory monitors #120242
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This commit cleans up the txn fingerprint ID cache in the following manner: - it properly performs the memory accounting for each id. Previously, we didn't connect the account to actual monitor (it was uninitialized) and we only grew by 1 byte (which is significant underestimate). We now remove unused monitor and create an account bound to the session monitor. - we now only store the id in the "key" part of the cache entry (previously we stored it also in "value" which was redundant). The main motivation for this change was reducing the memory leak that is (hopefully) fixed in the following commit. Release note: None
This commit - hopefully - fixes a memory leak that we observed around memory monitors when many new connections are established. The leak became possible to occur when we linked parent-child monitors together in b6d04fd. In particular, in that commit we introduced a way for a parent to track all of its children that haven't been stopped. Whenever a connection is stopped (i.e. the connExecutor exits), we stop its memory monitors, including `session root` monitor. Stopping that monitor should remove it from the list of children of `sql` monitor. However, we observed that for some reason the `session root` monitors are kept alive. In [this](#119799 (comment)) comment I outlined a hypothesis that it's due to a problem with Go GC marking in the presence of cyclical references. This commit removes some of those references which - hopefully - should allow Go GC to clean up old connections' monitors. In particular, whenever a monitor is stopped we now: - lose the reference to the head of the list of children as well as break the references between children themselves. In an ideal world, all children monitors should've been stopped already, so this change would be a noop, but as seen by the fix in the previous commit we forget to stop some monitors occassionally, so this change would make the code more bullet-proof. - set its `reserved` budget to `noReserved`, losing a possible reference to another monitor. This change makes sense on its own too. Release note (bug fix): A slow memory leak that can accumulate when opening many new connections has been fixed. The bug is present in 22.2.9+ and 23.1+ versions.
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Previously, `index-backfiller-merger-mon` memory monitor that is connected to the long-living backfiller monitor was never closed. As a result, these index-backfiller monitors would accumulate in its parent leading to a slow memory leak. Release note: None
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Mar 13, 2024
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Backport 3/3 commits from #119799 on behalf of @yuzefovich.
/cc @cockroachdb/release
See individual commits for details.
Epic: None
Release note (bug fix): A slow memory leak that can accumulate when opening many new connections has been fixed. The bug is present in 22.2.9+ and 23.1+ versions.
Release justification: bug fix.