Execute the no-dependent DDL job as soon as possible

[crazycs520]

Feature Request

Is your feature request related to a problem? Please describe:

test> admin show ddl jobs;
+--------+---------+-------------------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------+
| JOB_ID | DB_NAME | TABLE_NAME              | JOB_TYPE     | SCHEMA_STATE         | SCHEMA_ID | TABLE_ID | ROW_COUNT | START_TIME          | END_TIME            | STATE   |
+--------+---------+-------------------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------+
| 58     | test    | t                       | add index    | write reorganization | 1         | 56       | 0         | 2020-08-26 16:09:42 | <null>              | running |
| 59     | test    | t                       | add column   | none                 | 1         | 56       | 0         | 2020-08-26 16:09:44 | <null>              | none    |
| 61     | test    |                         | create table | none                 | 1         | 60       | 0         | 2020-08-26 16:09:47 | <null>              | none    |
+--------+---------+-------------------------+--------------+----------------------+-----------+----------+-----------+---------------------+---------------------+---------+

As you can see, DDL job 59 is blocked by DDL job 58, since they are both modify the table t, this is reasonable.

But DDL job 61 is also been blocked, it is blocked by DDL job 59, since they are in the same DDL job queue. This can be optimized because it doesn't have a dependent DDL job.

Implementation

In the function handleDDLJobQueue, we can change getFirstDDLJob into getFirstNoDependencyDDLJob to find the first job that has no dependency. We also need to handle the dequeue logic properly.

Score

300

SIG Slack Channel

You can join #sig-ddl on slack in your spare time to discuss and get help with mentors or others.

Mentor(s)

• @tangenta

Recommended Skills

• DDL
• Golang

Learning Materials

MySQL's document for syntax reference.
TiDB DDL architecture

[tangenta]

This issue is related to #32031.