SHOW VITESS_MIGRATION '...' LOGS, retain logs for 24 hours

[shlomi-noach]

Resubmission of #8493, for 11.0 release branch.

Description

Fixes #8178

• Support for show vitess_migration '<uuid>' logs queries, e.g. show vitess_migration '4835ca51_e867_11eb_ab12_0a43f95f28a3' logs
• Retaining migration logs for 24 hours after migration completion, whether migration is successful or not.

gh-ost and pt-osc (but not online) migrations generate a migration log, which Vitess stores in a well known location on the primary tablet.

It is now possible to view the file, during or after migration. The file is retained for 24 hours after completion/failure.

The command show vitess_migration '<uuid>' logs will output the entire log file content for each shard. Therefore, 4 shards => 4 log files.

This is tested in go/test/endtoend/onlineddl/ghost/onlineddl_ghost_test.go

Documentation to follow

Example:

mysql> show vitess_migration '3a273866_e867_11eb_ab12_0a43f95f28a3' logs \G
*************************** 1. row ***************************
migration_log: 2021-07-19 07:59:23 INFO starting gh-ost 261355426d8fc31b590733ca8ff8e79012103c18
2021-07-19 07:59:23 INFO Migrating `vt_commerce`.`corder`
2021-07-19 07:59:23 INFO executing gh-ost-on-startup hook: /tmp/online-ddl-3a273866_e867_11eb_ab12_0a43f95f28a3-943208852/gh-ost-on-startup
ok
2021-07-19 07:59:23 INFO inspector connection validated on ip-REDACTED:17100
2021-07-19 07:59:23 INFO User has SUPER, REPLICATION SLAVE privileges, and has ALL privileges on `vt_commerce`.*
2021-07-19 07:59:23 INFO binary logs validated on ip-REDACTED:17100
2021-07-19 07:59:23 INFO Restarting replication on ip-REDACTED:17100 to make sure binlog settings apply to replication thread
2021-07-19 07:59:23 INFO Inspector initiated on ip-REDACTED:17100, version 5.7.30-log
2021-07-19 07:59:23 INFO Table found. Engine=InnoDB
...

Related Issue(s)

• Online DDL: allow users to see migration log (in case of migration failure) #8178
• Online DDL: tracking issue #6926

Checklist

• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes