br: fix panic during merging files

[YuJuncen]

Signed-off-by: Yu Juncen [email protected]

What problem does this PR solve?

Issue Number: close #33801

Problem Summary:
The merge small files operation may panic because it try to decode the index value, however the region boundary is sometime weird and make TiDB panic.

What is changed and how it works?

This PR use DecodeKeyHead to replace DecodeIndexKey, which won't try to decode the index value.

Check List

Tests

• Unit test
  A fuzz test shows that this change is probably panic-free:

> go test -fuzz=FuzzMerge br/pkg/restore/merge_fuzz_test.go
fuzz: elapsed: 0s, gathering baseline coverage: 0/81 completed
fuzz: elapsed: 3s, gathering baseline coverage: 81/81 completed, now fuzzing with 17 workers
fuzz: elapsed: 3s, execs: 81 (27/sec), new interesting: 0 (total: 81)
fuzz: elapsed: 6s, execs: 8727 (2883/sec), new interesting: 5 (total: 86)
fuzz: elapsed: 9s, execs: 17959 (3077/sec), new interesting: 12 (total: 93)
fuzz: elapsed: 12s, execs: 47126 (9724/sec), new interesting: 20 (total: 101)
fuzz: elapsed: 15s, execs: 65828 (6234/sec), new interesting: 23 (total: 104)
fuzz: elapsed: 18s, execs: 88492 (7553/sec), new interesting: 25 (total: 106)
fuzz: elapsed: 21s, execs: 105989 (5833/sec), new interesting: 25 (total: 106)
fuzz: elapsed: 24s, execs: 151362 (15123/sec), new interesting: 28 (total: 109)
fuzz: elapsed: 27s, execs: 183271 (10637/sec), new interesting: 29 (total: 110)
fuzz: elapsed: 30s, execs: 216909 (11214/sec), new interesting: 31 (total: 112)
fuzz: elapsed: 33s, execs: 254825 (12636/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 36s, execs: 278409 (7863/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 39s, execs: 325000 (15529/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 42s, execs: 346768 (7255/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 45s, execs: 367738 (6991/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 48s, execs: 406754 (13006/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 51s, execs: 424218 (5819/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 54s, execs: 439857 (5214/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 57s, execs: 459651 (6597/sec), new interesting: 35 (total: 116)
fuzz: elapsed: 1m0s, execs: 480267 (6873/sec), new interesting: 35 (total: 116)
^Cfuzz: elapsed: 1m1s, execs: 485575 (5989/sec), new interesting: 35 (total: 116)

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

Release note

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

Fix a bug that caused BR panics sometime when merge small file enabled.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• fengou1

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After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/b7d457e35808b820dbe20136744797edb6534057

[YuJuncen]

/run-unit-test

[joccau]

/run-integration-br-test

[3pointer]

LGTM, well done

[fengou1]

LGTM

[kennytm]

/merge

[ti-chi-bot]

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

Commit hash: b7d457e

[YuJuncen]

/run-integration-br-tests

[ti-srebot]

cherry pick to release-5.3 in PR #34017

[ti-srebot]

cherry pick to release-5.4 in PR #34019

[ti-srebot]

cherry pick to release-6.0 in PR #34020

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! [1] CI still failing after this pr merged.
These failed integration tests don't seem to be introduced by the current PR.

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/code-coverage	🔴 unit test failed, coverage data was not available	13 min	Existing failure
idc-jenkins-ci-tidb/integration-br-test	🟢 all 29 tests passed	42 min	Existing passed
idc-jenkins-ci/integration-cdc-test	🟢 all 34 tests passed	41 min	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	23 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 11 tests passed	15 min	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	14 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	14 min	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	14 min	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	13 min	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	12 min	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	5 min 41 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed