Lazy constraint check may cause data inconsistency

[zyguan]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

/* t */ drop table if exists t;
/* t */ create table t (c0 int, c1 varchar(20), c2 varchar(20), unique key(c0), key(c2));
/* t */ insert into t (c0, c1, c2) values (1, null, 'green');

/* t */ set tidb_constraint_check_in_place=0;
/* t */ begin optimistic;
/* t */ insert into t (c0, c1, c2) values (1, 'red', 'white');
/* t */ delete from t where c1 is null;
/* t */ update t set c2 = 'green' where c2 between 'purple' and 'white';
/* t */ commit;
/* t */ admin check table t;

Note that tidb_constraint_check_in_place is off by default!

2. What did you expect to see? (Required)

No error reported by admin check table.

3. What did you see instead (Required)

/* t */ admin check table t;
-- t >> E8133: handle 1, index:types.Datum{k:0x1, decimal:0x0, length:0x0, i:1, collation:"", b:[]uint8(nil), x:interface {}(nil)} != record:<nil>

4. What is your TiDB version? (Required)

master (2844660)

[cfzjywxk]

The default tidb_constraint_check_in_place value is 0 so the set tidb_constraint_check_in_place=0; set statement is not a must to reproduce the issue.

[zyguan]

The default tidb_constraint_check_in_place value is 0 so the set tidb_constraint_check_in_place=0; set statement is not a must to reproduce the issue.

Yes, I just mean to address it.

[cfzjywxk]

The untouched keys would be skipped in the commit phase, some keys could be marked with untouched flags in the memory buffer but the existence check for them is not done yet, these keys could not be skipped when the optimistic transaction is used.

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.

[zyguan]

#30447 has been cherry-picked to all release branches and these PRs are waiting for triage. We can close this issue now.

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.