ddl, util/codec: fix add index OOM and prevent panic in logging (#29925)

[ti-srebot]

cherry-pick #29925 to release-5.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/30126

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git push git@github.com:ti-srebot/tidb.git pr/30126:release-5.2-d04a1285a54c

---

What problem does this PR solve?

Issue Number: close #27687

Reproducible step:

drop table if exists t;
create table t (a bigint primary key);
insert into t values (-9078130948872077313);
alter table t add index idx(a);

Problem Summary:

This problem may occur in the following conditions:

• The table contains an clustered integer primary key.
  • If it is unsigned, at least one large primary key(> MaxInt64) is explicitly inserted.
  • If it is signed, at least one small negative number is explicitly inserted.
• An adding index job is running.

There is a bug in the current implementation of NewCommonHandle():

tidb/kv/key.go

Lines 237 to 262 in 37bfd57

	// NewCommonHandle creates a CommonHandle from a encoded bytes which is encoded by code.EncodeKey.
	func NewCommonHandle(encoded []byte) (*CommonHandle, error) {
	ch := &CommonHandle{encoded: encoded}
	if len(encoded) < 9 {
	padded := make([]byte, 9)
	copy(padded, encoded)
	ch.encoded = padded
	}
	remain := encoded
	endOff := uint16(0)
	for len(remain) > 0 {
	if remain[0] == 0 {
	// padded data
	break
	}
	var err error
	var col []byte
	col, remain, err = codec.CutOne(remain)
	if err != nil {
	return nil, err
	}
	endOff += uint16(len(col))
	ch.colEndOffsets = append(ch.colEndOffsets, endOff)
	}
	return ch, nil
	}

If the argument bytes have a prefix like 0x8203, CutOne() cuts nothing so that the remain is unchanged in the loop. This dead loop may cause TiDB OOM quickly because it endlessly append() colEndOffsets.

What is changed and how it works?

1. The function peek() in the decoding process does not handle the invalid key. It is possible to run into a dead loop and makes TiDB OOM.
2. The function tryDecodeHandleToString() is only used for logging, it should be wrapped with recover() so that the critical operation is not interrupted.

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

Fix an issue that adding index panics by chance.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• wjhuang2016
• zimulala

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[ti-srebot]

/run-all-tests

[ti-srebot]

@tangenta you're already a collaborator in bot's repo.

[zimulala]

LGTM

[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

• https://prow.tidb.io/command-help#cherrypick
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• https://internals.tidb.io/t/topic/785