Less contention in cache, part 4

[kssenii]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Less contention in filesystem cache (part 4). Allow to keep filesystem cache not filled to the limit by doing additional eviction in the background (controlled by keep_free_space_size(elements)_ratio). This allows to release pressure from space reservation for queries (on tryReserve method). Also this is done in a lock free way as much as possible, e.g. should not block normal cache usage.

Contains commits from #61163, so should be merged/reviewed after.

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[robot-ch-test-poll]

This is an automated comment for commit 3f9ca1c with description of existing statuses. It's updated for the latest CI running

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Check name	Description	Status
AST fuzzer	Runs randomly generated queries to catch program errors. The build type is optionally given in parenthesis. If it fails, ask a maintainer for help	❌ failure
CI running	A meta-check that indicates the running CI. Normally, it's in success or pending state. The failed status indicates some problems with the PR	⏳ pending
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[jkartseva]

I'm not sure if it's a realistic scenario: if a task fails to free up the space repetitively (collectCandidatesForEviction returns false), it will be re-scheduled for immediate processing. Can it stuck in this state?

[kssenii]

Yes, it is not a realistic scenario that we fail to free up required space because of not enough evictable/freeable cache entries, but limits_satisfied will also be false if we did not free up all the needed space because of the eviction batch size (by default it is quite small), so I thought it makes sense to schedule immediately in this case. I do not think it can get stuck in this state because this could possibly happen if cache constantly grows in size at a high speed, but in this case we should also get into lock contention case and get into another reschedule here:

ClickHouse/src/Interpreters/Cache/FileCache.cpp

Lines 969 to 973 in 3e4d9bf

	auto lock = tryLockCache();
	/// To avoid deteriorating contention on cache,
	/// proceed only if cache is not heavily used.
	if (!lock)

I will add profile event for the number of eviction tries, so we will be able to see if it is stuck in constant reschedule on the dashboard.

[kssenii]

Looks like 02967_analyzer_fuzz is broken, but not related to changes (#63264)

Stateless tests (asan) [3/4] — fail: 1

02967_analyzer_fuzz

Stateless tests (debug) [4/5] — fail: 1

02967_analyzer_fuzz

Stateless tests (release) — fail: 1, passed: 6497, skipped: 12

02967_analyzer_fuzz

Stateless tests (tsan) [4/5] — fail: 1, passed: 1244, skipped: 18

02967_analyzer_fuzz

Stateless tests (ubsan) [1/2] — fail: 1, passed: 3201, skipped: 31

02967_analyzer_fuzz

Upgrade check (debug) — New settings are not reflected in settings changes history

It complains about:

   ┌─name──────────────────────────────┐
1. │ allow_experimental_join_condition │
   └───────────────────────────────────┘

so not related to changes as well

AST fuzzer (ubsan)

#56640