index data may be lost when creating expression index

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE `t` (
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL
);

insert into t many rows (about 1 000 000)
/* DDL */ alter table t add index id2xx((b+1));
                                    /* txn during DDL */ begin pessimistic;
                                    /* txn during DDL */ insert into t values (52000003, 503);
                                    /* txn  during DDL */  commit;
/* DDL */ finish DDL
mysql> admin check table t;
ERROR 8134 (HY000): col _V$_id2xx_0, handle 686873, index:types.Datum{k:0x0, decimal:0x0, length:0x0, i:0, collation:"", b:[]uint8(nil), x:interface {}(nil)} != record:types.Datum{k:0x1, decimal:0x0, length:0x0, i:504, collation:"", b:[]uint8(nil), x:interface {}(nil)}, compare err:<nil>

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

No error

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master

[ChenPeng2013]

because expression index is experimental feature, severity is set to major

[cfzjywxk]

@wjhuang2016
The current implementation of transaction amend is not compatible with expression index, it's needed to reject the amend path for expression index at https://github.com/pingcap/tidb/blob/master/session/schema_amender.go#L220.Also some compatibility test case are needed to verify the rejection.

[wjhuang2016]

It has nothing to do with amending txn.

[ti-srebot]

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