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Optimize apply speed under heavy write pressure (#4883) #5668

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This is an automated cherry-pick of #4883

What problem does this PR solve?

Issue Number: ref #4728

Problem Summary: When tiflash is under heavy write pressure, it will consume a lot of write throughput and cause some latency on the process of apply raft log, which will make tiflash consume a log memory.

What is changed and how it works?

  1. Only allow one delta flush process on a segment to process at any time to avoid unnecessary throughput consumption;
  2. When processing CompactLog raft command, just try to flush the unsaved value in storage once and return Persist if the flush succed or None if the flush failed.(Originally we try to flush until it success)
  3. Increase foreground flush threshold for write thread.
  4. Avoid add minor compaction task to background if the segment is flushing to save some throughput and reduce lock contention on the segment.

Check List

Tests

  • Manual test (add detailed scripts or steps below)
    Test step:
  1. perform large transaction update through 5 tidb instance at the same time and the total transaction size of all tidb instance is about 24.5 GB;
    Before optimize:
    image
    After optimize:
    image

Detail result(unit: GB)

  1st run 2nd run 3rd run 4th run 5th run 6th run) 7th run average value amplification factor
before optimization 40.8 37.2 37.3 36 34.7 33.6 34.5 36.3 1.48
after optimization 38.1 29.4 29 34.3 29.6 32.6 37.7 32.9 1.34

Side effects

  • Performance regression: Consumes more CPU
  • Performance regression: Consumes more Memory
  • Breaking backward compatibility

Documentation

  • Affects user behaviors
  • Contains syntax changes
  • Contains variable changes
  • Contains experimental features
  • Changes MySQL compatibility

Release note

None

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>
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ti-chi-bot commented Aug 22, 2022

[REVIEW NOTIFICATION]

This pull request has been approved by:

  • CalvinNeo

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
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@ti-chi-bot ti-chi-bot added release-note-none Denotes a PR that doesn't merit a release note. do-not-merge/cherry-pick-not-approved size/L Denotes a PR that changes 100-499 lines, ignoring generated files. type/cherry-pick-for-release-6.1 This PR is cherry-picked to release-6.1 from a source PR. labels Aug 22, 2022
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@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

@ti-chi-bot ti-chi-bot added the status/LGT1 Indicates that a PR has LGTM 1. label Aug 22, 2022
@lidezhu lidezhu closed this Aug 22, 2022
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3 participants