*: avoid thundering herd problem when timeout the stats sync load #50956
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Signed-off-by: Weizhen Wang <wangweizhen@pingcap.com>
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Signed-off-by: Weizhen Wang <wangweizhen@pingcap.com>
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Additional details and impacted files@@ Coverage Diff @@
## master #50956 +/- ##
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+ Coverage 72.2645% 72.5844% +0.3199%
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Files 1466 1466
Lines 361209 434144 +72935
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+ Hits 261026 315121 +54095
- Misses 80918 99112 +18194
- Partials 19265 19911 +646
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| @@ -196,7 +197,10 @@ func (s *statsSyncLoad) SubLoadWorker(sctx sessionctx.Context, exit chan struct{ | |||
| case errExit: | |||
| return | |||
| default: | |||
| time.Sleep(s.statsHandle.Lease() / 10) | |||
| // To avoid the thundering herd effect | |||
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It seems that sync load tasks are processed sequentially here, and a single sync load task is not concurrent. So why does the thundering herd effect occur?
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stats-load-concurrency controls the concurrency of sync load. at default, it will create 5 concurrency to work for it.
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so if we have a large tidb cluster, it is easy that many node have to retry at the same time.
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: AilinKid, elsa0520, winoros The full list of commands accepted by this bot can be found here. The pull request process is described here
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/cherrypick release-7.5 |
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@hawkingrei: new pull request created to branch In response to this:
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What problem does this PR solve?
Issue Number: close #50957
Problem Summary:
What changed and how does it work?
we need to load the stats cache in the background. but if we meet the timeout, we must wait constantly to retry. it will happen thundering herd. so we need to add the rand sleep to prevent it.
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