Change a json column using DML statements will lead to change of the column meta data

[zyguan]

Description

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Enable amend transaction by set tidb_enable_amend_pessimistic_txn to 1, and execute following sql

/* INIT */ drop table if exists t;
/* INIT */ create table t (id int primary key, c_json json);
/* INIT */ insert into t values (1, '{"k": 1}');
/* TXN */ begin;
/* DDL */ alter table t rename column c_json to cc_json;
/* TXN */ update t set c_json = '{"k": 2}' where id = 1;
/* TXN */ commit;

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

Transaction should be committed successfully.

3. What did you see instead (Required)

Error 8028: Information schema is changed during the execution of the statement(for example, table definition may be updated by other DDL ran in parallel). If you see this error often, try increasing `tidb_max_delta_schema_count`. [try again later]

4. What is your TiDB version? (Required)

master @ a363130

SIG slack channel

#sig-exec

Score

• 300

Mentor

• @SunRunAway

[cfzjywxk]

This is caused by the update statement which uses BuildCastFunction to build a castAsJSONFunctionClass function, whose getFunction add a flag mysql.ParseToJSONFlag to the schema meta column info. This implicitly changes the schema meta data.
@XuHuaiyu PTAL

[bb7133]

The statements described in 'Minimal reproduce step' should be in different sessions, right? @zyguan

[zyguan]

The statements described in 'Minimal reproduce step' should be in different sessions, right? @zyguan

@bb7133 Yes, each tag in block comments (eg. /* DDL */) indicates a session. I've implement a simple tool to execute it. https://github.com/zyguan/sqlz/tree/stmtflow/examples/stmtflow