| Bug #96042 | metadata lock waiting | ||
|---|---|---|---|
| Submitted: | 1 Jul 2019 8:00 | Modified: | 1 Jul 2019 13:07 |
| Reporter: | chunyang xu | Email Updates: | |
| Status: | Not a Bug | Impact on me: | |
| Category: | MySQL Server | Severity: | S3 (Non-critical) |
| Version: | 5.7.18 | OS: | Any |
| Assigned to: | CPU Architecture: | Any | |
| Tags: | Metadata lock, rollback | ||
[1 Jul 2019 13:07]
MySQL Verification Team
Hi Mr. Xu, Thank you for your bug report. However, this is not a bug. This is exactly why MDL were invented and implemented in the SQL layer. Those were invented so that DDL operations would prevent InnoDB SE from changing data, while DDL is in progress. The only thing that you can do is to make 100 % sure that lock_wait_timeout (which refers to MDL) is much larger then innodb_lock_wait_timeout (which is InnoDB SE specific), That is all that you can do. This is all fully described in our Reference Manual.
Description: when alter a table , it can't finish successfuly. waiting acquire a metadata lock . How to repeat: session A: mysql> create table xcy_test_utf8( id int , -> name varchar(2), -> addr varchar(200)); mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> insert into xcy_test_utf8 values(1,'xcy','beijing'); ERROR 1406 (22001): Data too long for column 'name' at row 1 then , Session B try to modify the table xcy_test_utf8 struct, want to extend the name column size. SESSION B: alter table xcy_test_utf8 modify name varchar(30); AND THEN. the status of session B is "Waiting for table metadata lock" if use the command "show engine innodb status " to check if exists active session , but can't find it . if use the command "select * from information_schema.innodb_trx " to check if exists active session , no rows about it . Suggested fix: if a sql faild , should release metadata lock about it .