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planner: fix the wrong cost formula for MPP net cost #32942

Merged
merged 17 commits into from
Mar 14, 2022
Merged

planner: fix the wrong cost formula for MPP net cost #32942

merged 17 commits into from
Mar 14, 2022

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qw4990
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@qw4990 qw4990 commented Mar 9, 2022

What problem does this PR solve?

Issue Number: close #30103

Problem Summary: planner: fix the wrong cost formula for MPP net cost

What is changed and how it works?

The original MPP net cost formula doesn't consider rowSize/rowWidth, this PR fixes it.

Check List

Tests

  • Unit test
  • Integration test
  • Manual test (add detailed scripts or steps below)
  • No code

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

planner: fix the wrong cost formula for MPP net cost

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ti-chi-bot commented Mar 9, 2022 •
edited

[REVIEW NOTIFICATION]

This pull request has been approved by:

  • Reminiscent
  • time-and-fate

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@ti-chi-bot ti-chi-bot added release-note size/M Denotes a PR that changes 30-99 lines, ignoring generated files. labels Mar 9, 2022
@qw4990 qw4990 added sig/planner SIG: Planner type/bug-fix This PR fixes a bug. type/enhancement and removed size/M Denotes a PR that changes 30-99 lines, ignoring generated files. type/bug-fix This PR fixes a bug. labels Mar 9, 2022
@ti-chi-bot ti-chi-bot added the size/M Denotes a PR that changes 30-99 lines, ignoring generated files. label Mar 9, 2022
@ti-chi-bot ti-chi-bot added size/L Denotes a PR that changes 100-499 lines, ignoring generated files. and removed size/M Denotes a PR that changes 30-99 lines, ignoring generated files. labels Mar 10, 2022
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sre-bot commented Mar 10, 2022 •
edited

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/f9c186c24de87b9098254b1be00fc297388481fd

Reminiscent
Reminiscent reviewed Mar 10, 2022
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planner/core/task.go
if p.ctx.GetSessionVars().IsMPPEnforced() {
p.cost = cst / 1000000000
cst /= 1000000000
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Should the p.cost /= 1000000000 at the same time(like the previous)?

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I think we don't need to change p.cost here since cst is the one that used to be compared with other plan costs so we have to change it to make the planner choose this plan.
Keeping p.cost unchanged here can let us know the real cost of the plan when using explain format=verbose, and the new test TestRowSizeInMPP relies on this.

@ti-chi-bot ti-chi-bot added status/LGT1 Indicates that a PR has LGTM 1. needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. labels Mar 10, 2022
@ti-chi-bot ti-chi-bot added status/LGT2 Indicates that a PR has LGTM 2. and removed status/LGT1 Indicates that a PR has LGTM 1. labels Mar 11, 2022
@ti-chi-bot ti-chi-bot added size/M Denotes a PR that changes 30-99 lines, ignoring generated files. and removed needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. labels Mar 14, 2022
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qw4990 commented Mar 14, 2022

/run-unit-test

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qw4990 commented Mar 14, 2022

/merge

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This pull request has been accepted and is ready to merge.

Commit hash: f9c186c

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Mar 14, 2022
@ti-chi-bot ti-chi-bot merged commit f0238dd into pingcap:master Mar 14, 2022
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@time-and-fate time-and-fate time-and-fate approved these changes

@Reminiscent Reminiscent Reminiscent approved these changes

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release-note sig/planner SIG: Planner size/M Denotes a PR that changes 30-99 lines, ignoring generated files. status/can-merge Indicates a PR has been approved by a committer. status/LGT2 Indicates that a PR has LGTM 2. type/enhancement
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Successfully merging this pull request may close these issues.

The formula of calculating net cost for TiFlash plans is not aligned with TiKV plans'
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