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sessionctx/stmtctx: do not use copy-on-read for GetWarnings function #39742

Merged
merged 5 commits into from
Dec 9, 2022
Merged

sessionctx/stmtctx: do not use copy-on-read for GetWarnings function #39742

merged 5 commits into from
Dec 9, 2022

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tiancaiamao
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What problem does this PR solve?

Issue Number: close #39702

Problem Summary:

What is changed and how it works?

7 min 53s => 9.32s
(B.T.W, if we don't add error stack on decimal truncate error, the execution time can furthur reduce to 5s)

image

Before the change:

mysql> insert into t1 (c1) select * from t2;
Query OK, 491520 rows affected, 65535 warnings (7 min 53.87 sec)
Records: 491520  Duplicates: 0  Warnings: 65535

After:

mysql> insert into t1 (c1) select * from t2;
Query OK, 491520 rows affected, 65535 warnings (9.32 sec)
Records: 491520  Duplicates: 0  Warnings: 65535

Check List

Tests

  • Unit test
  • Integration test
  • Manual test (add detailed scripts or steps below)

See #39702 reproduce process.

  • 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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

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ti-chi-bot commented Dec 7, 2022 •
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[REVIEW NOTIFICATION]

This pull request has been approved by:

  • Defined2014
  • hawkingrei

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@ti-chi-bot ti-chi-bot added release-note-none Denotes a PR that doesn't merit a release note. size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Dec 7, 2022
Defined2014
Defined2014 reviewed Dec 8, 2022
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sessionctx/stmtctx/stmtctx.go
warns := make([]SQLWarn, len(sc.mu.warnings))
copy(warns, sc.mu.warnings)
return warns
return sc.mu.warnings
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Will return warnings directly cause conflict?

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This code date back to very early commit:

5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 407) // GetWarnings gets warnings.
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 408) func (sc *StatementContext) GetWarnings() []error {
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 409)        sc.mu.Lock()
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 410)        warns := make([]error, len(sc.mu.warnings))
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 411)        copy(warns, sc.mu.warnings)
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 412)        sc.mu.Unlock()
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 413)        return warns
5230f5eabd7 (Ewan Chou    2016-11-29 14:25:38 +0800 414) }

The commit is sooooooo old that it's hard to figure out why it's written like that.

The change should work, if not, at least we can see where the data race happen and try to fix again.
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without copy, does the lock necessary here?

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without copy, does the lock necessary here?

I think so ... GetWarnings / SetWarnings may be visited by many different component, maybe concurrently.

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Got it. The value of sc.mu.warnings will be changed by SetWarnings.

@ti-chi-bot ti-chi-bot added the status/LGT1 Indicates that a PR has LGTM 1. label Dec 9, 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 Dec 9, 2022
@tiancaiamao
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/merge

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

Commit hash: 1688e68

@ti-chi-bot ti-chi-bot added the status/can-merge Indicates a PR has been approved by a committer. label Dec 9, 2022
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/run-mysql-test
/run-unit-test

@ti-chi-bot ti-chi-bot merged commit 96eb4ba into pingcap:master Dec 9, 2022
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sre-bot commented Dec 9, 2022

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name Result Duration Compare with Parent commit
idc-jenkins-ci/integration-cdc-test 🟥 failed 3, success 37, total 40 24 min New failing
idc-jenkins-ci-tidb/common-test 🔴 failed 1, success 10, total 11 4 min 40 sec Existing failure
idc-jenkins-ci-tidb/integration-common-test ✅ all 17 tests passed 18 min Fixed
idc-jenkins-ci-tidb/mybatis-test ✅ all 1 tests passed 3 min 29 sec Fixed
idc-jenkins-ci-tidb/tics-test 🟢 all 1 tests passed 7 min 44 sec Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2 🟢 all 28 tests passed 6 min 11 sec Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1 🟢 all 26 tests passed 5 min 23 sec Existing passed
idc-jenkins-ci-tidb/integration-ddl-test 🟢 all 6 tests passed 5 min 8 sec Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test 🟢 all 1 tests passed 3 min 23 sec Existing passed
idc-jenkins-ci-tidb/plugin-test 🟢 build success, plugin test success 4min Existing passed

@tiancaiamao tiancaiamao deleted the issue-39702 branch December 14, 2022 07:06
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@hawkingrei hawkingrei hawkingrei approved these changes

@Defined2014 Defined2014 Defined2014 approved these changes

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Extremely inefficient GetWarnings() makes the query slow
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