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Vitess provides two interfaces to interacting with Online DDL:
- SQL commands, via
VTGate - Command line interface, via
vtctl
Supported interactions are:
- Running migrations (submitting Online DDL requests)
- Tracking migrations
- Launching a migration or all migrations, if explicitly set to postpone launch.
- Completing a migration or all migrations, if explicitly set to postpone completion.
- Cancelling a migration
- Cancelling a migration
- Cancelling all pending migrations
- Retrying a migration
- Cleaning migration artifacts
- Reverting a migration
Running migrations
To run a managed schema migration, you should:
- Formulate your DDLs (
CREATE,ALTER,DROP) queries - Choose a ddl_strategy
When the user submits an online DDL, Vitess responds with a UUID, a job Id used to later track or control the migration. The migration does not start immediately. It is queued at the tablets and executed at some point in the future.
Via VTGate/SQL
mysql> set @@ddl_strategy='vitess';mysql> alter table corder add column ts timestamp not null default current_timestamp;+--------------------------------------+| uuid |+--------------------------------------+| bf4598ab_8d55_11eb_815f_f875a4d24e90 |+--------------------------------------+mysql> drop table customer;+--------------------------------------+| uuid |+--------------------------------------+| 6848c1a4_8d57_11eb_815f_f875a4d24e90 |+--------------------------------------+
@@ddl_strategybehaves like a MySQL session variable, though is only recognized byVTGate. Setting@@ddl_strategyonly applies to that same connection and does not affect other connections. The strategy applies to all migrations executed in that session. You may subsequently set@@ddl_strategyto different value.- If you run
vtgatewithout--ddl_strategy, then@@ddl_strategydefaults to'direct', which implies schema migrations are synchronous. You will need toset @@ddl_strategy='gh-ost'to run followupALTER TABLEstatements viagh-ost. - If you run
vtgate --ddl_strategy "gh-ost", then@@ddl_strategydefaults to'gh-ost'in each new session. AnyALTER TABLEwill run viagh-ost. You mayset @@ddl_strategy='pt-osc'to make migrations run throughpt-online-schema-change, orset @@ddl_strategy='direct'to run migrations synchronously.
Via vtctlclient/ApplySchema
You may use vtctl or vtctlclient (the two are interchangeable for the purpose of this document) to apply schema changes. The ApplySchema command supports both synchronous and online schema migrations. To run an online schema migration you will supply the --ddl_strategy command line flag:
$ vtctlclient -- ApplySchema --ddl_strategy "vitess" --sql "ALTER TABLE demo MODIFY id bigint UNSIGNED" commercea2994c92_f1d4_11ea_afa3_f875a4d24e90
You my run multiple migrations withing the same ApplySchema command:
$ vtctlclient -- ApplySchema --skip_preflight --ddl_strategy "vitess" --sql "ALTER TABLE demo MODIFY id bigint UNSIGNED; CREATE TABLE sample (id int PRIMARY KEY); DROP TABLE another;" commerce3091ef2a_4b87_11ec_a827_0a43f95f28a3
ApplySchema accepts the following flags:
--ddl_strategy: by default migrations run directly via MySQL standard DDL. This flag must be aupplied to indicate an online strategy. See also DDL strategies and ddl_strategy flags.--migration_context <unique-value>: all migrations in aApplySchemacommand are logically grouped via a unique context. A unique value will be supplied automatically. The user may choose to supply their own value, and it’s their responsibility to provide with a unique value. Any string format is accepted. The context can then be used to search for migrations, viaSHOW VITESS_MIGRATIONS LIKE 'the-context'. It is visible inSHOW VITESS_MIGRATIONS ...output as themigration_contextcolumn.--skip_preflight: skip an internal Vitess schema validation. When running an online DDL it’s recommended to add--skip_preflight. In future Vitess versions this flag may be removed or default totrue.
Tracking migrations
You may track the status of a single or of multiple migrations. Since migrations run asycnhronously, it is the user’s responsibility to audit the progress and state of submitted migrations. Users are likely to want to know when a migration is complete (or failed) so as to be able to deploy code changes or run other operations.
Common patterns are:
- Show state of a specific migration
- Show all
running,completeorfailedmigrations - Show recent migrations
- Show migrations ordered by most-recent first.
- Show n number of migrations, skipping m rows.
Via VTGate/SQL
Examples for a single shard cluster:
mysql> show vitess_migrations like 'bf4598ab_8d55_11eb_815f_f875a4d24e90' \G*************************** 1. row ***************************id: 23migration_uuid: bf4598ab_8d55_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: cordermigration_statement: alter table corder add column ts timestamp not null default current_timestamp()strategy: vitessoptions:added_timestamp: 2021-03-25 12:35:01requested_timestamp: 2021-03-25 12:34:58ready_timestamp: 2021-03-25 12:35:04started_timestamp: 2021-03-25 12:35:04liveness_timestamp: 2021-03-25 12:35:06completed_timestamp: 2021-03-25 12:35:06cleanup_timestamp: NULLmigration_status: completelog_path:artifacts: _bf4598ab_8d55_11eb_815f_f875a4d24e90_20210325123504_vrepl,retries: 0tablet: zone1-0000000100tablet_failure: 0progress: 100migration_context: vtgate:a8352418-8d55-11eb-815f-f875a4d24e90ddl_action: altermessage:eta_seconds: 0
mysql> show vitess_migrations like 'complete' \G...*************************** 21. row ***************************id: 24migration_uuid: 6848c1a4_8d57_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: customermigration_statement: drop table customerstrategy: vitessoptions:added_timestamp: 2021-03-25 12:46:53requested_timestamp: 2021-03-25 12:46:51ready_timestamp: 2021-03-25 12:46:57started_timestamp: 2021-03-25 12:46:57liveness_timestamp: 2021-03-25 12:46:57completed_timestamp: 2021-03-25 12:46:57cleanup_timestamp: NULLmigration_status: completelog_path:artifacts: _vt_HOLD_6848c1a48d5711eb815ff875a4d24e90_20210326104657,retries: 0tablet: zone1-0000000100tablet_failure: 0progress: 100migration_context: vtgate:a8352418-8d55-11eb-815f-f875a4d24e90ddl_action: dropmessage:eta_seconds: 0
mysql> show vitess_migrations where completed_timestamp > now() - interval 1 day;+----+--------------------------------------+----------+-------+--------------+-------------+---------------------------------------------------------------------------------+----------+---------+---------------------+---------------------+---------------------+---------------------+---------------------+---------------------+-------------------+------------------+----------+-------------------------------------------------------------+---------+------------------+----------------+----------+---------------------------------------------+------------+---------+-------------+| id | migration_uuid | keyspace | shard | mysql_schema | mysql_table | migration_statement | strategy | options | added_timestamp | requested_timestamp | ready_timestamp | started_timestamp | liveness_timestamp | completed_timestamp | cleanup_timestamp | migration_status | log_path | artifacts | retries | tablet | tablet_failure | progress | migration_context | ddl_action | message | eta_seconds |+----+--------------------------------------+----------+-------+--------------+-------------+---------------------------------------------------------------------------------+----------+---------+---------------------+---------------------+---------------------+---------------------+---------------------+---------------------+-------------------+------------------+----------+-------------------------------------------------------------+---------+------------------+----------------+----------+---------------------------------------------+------------+---------+-------------+| 23 | bf4598ab_8d55_11eb_815f_f875a4d24e90 | commerce | 0 | vt_commerce | corder | alter table corder add column ts timestamp not null default current_timestamp() | online | | 2021-03-25 12:35:01 | 2021-03-25 12:34:58 | 2021-03-25 12:35:04 | 2021-03-25 12:35:04 | 2021-03-25 12:35:06 | 2021-03-25 12:35:06 | NULL | complete | | _bf4598ab_8d55_11eb_815f_f875a4d24e90_20210325123504_vrepl, | 0 | zone1-0000000100 | 0 | 100 | vtgate:a8352418-8d55-11eb-815f-f875a4d24e90 | alter | | 0 || 24 | 6848c1a4_8d57_11eb_815f_f875a4d24e90 | commerce | 0 | vt_commerce | customer | drop table customer | online | | 2021-03-25 12:46:53 | 2021-03-25 12:46:51 | 2021-03-25 12:46:57 | 2021-03-25 12:46:57 | 2021-03-25 12:46:57 | 2021-03-25 12:46:57 | NULL | complete | | _vt_HOLD_6848c1a48d5711eb815ff875a4d24e90_20210326104657, | 0 | zone1-0000000100 | 0 | 100 | vtgate:a8352418-8d55-11eb-815f-f875a4d24e90 | drop | | 0 || 25 | 6fd57dd3_8d57_11eb_815f_f875a4d24e90 | commerce | 0 | vt_commerce | customer | revert 6848c1a4_8d57_11eb_815f_f875a4d24e90 | online | | 2021-03-25 12:47:08 | 2021-03-25 12:47:04 | 2021-03-25 12:47:12 | 2021-03-25 12:47:12 | 2021-03-25 12:47:12 | 2021-03-25 12:47:12 | NULL | complete | | _vt_HOLD_6848c1a48d5711eb815ff875a4d24e90_20210326104657, | 0 | zone1-0000000100 | 0 | 100 | vtgate:a8352418-8d55-11eb-815f-f875a4d24e90 | create | | 0 |+----+--------------------------------------+----------+-------+--------------+-------------+---------------------------------------------------------------------------------+----------+---------+---------------------+---------------------+---------------------+---------------------+---------------------+---------------------+-------------------+------------------+----------+-------------------------------------------------------------+---------+------------------+----------------+----------+---------------------------------------------+------------+---------+-------------+
show vitess_migrationsshows the entire history of migrations.show vitess_migrations like ...filters migrations bymigration_uuid, ormigration_context, ormigration_status.show vitess_migrations where ...lets the user specify arbitrary conditions.- All commands return results for the keyspace (schema) in use.
Via vtctlclient/ApplySchema
Examples for a 4-shard cluster:
$ vtctlclient OnlineDDL commerce show ab3ffdd5_f25c_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000201 | 40-80 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:24:33 | 2020-09-09 05:24:34 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000401 | c0- | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000101 | -40 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce show 8a797518_f25c_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000401 | c0- | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | running || test-0000000201 | 40-80 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | 2020-09-09 05:23:33 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | running || test-0000000101 | -40 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | running |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce show 8a797518_f25c_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000401 | c0- | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000101 | -40 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000201 | 40-80 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | 2020-09-09 05:23:33 | complete |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce show recent+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000201 | 40-80 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | 2020-09-09 05:23:33 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:24:33 | 2020-09-09 05:24:34 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000301 | 80-c0 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000401 | c0- | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000401 | c0- | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000401 | c0- | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000101 | -40 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000101 | -40 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000101 | -40 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL --order descending commerce show all+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000101 | -40 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000101 | -40 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000101 | -40 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000401 | c0- | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000401 | c0- | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000401 | c0- | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:24:33 | 2020-09-09 05:24:34 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | 2020-09-09 05:23:33 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce show failed+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000401 | c0- | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000101 | -40 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL --limit 5 commerce show recent+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000201 | 40-80 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | 2020-09-09 05:23:33 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:24:33 | 2020-09-09 05:24:34 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL --skip 5 --limit 5 commerce show recent+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000401 | c0- | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:25:13 | 2020-09-09 05:25:14 | complete || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 8a797518_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:23:32 | | failed || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 63b5db0c_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:22:41 | 2020-09-09 05:22:42 | complete || test-0000000201 | 40-80 | vt_commerce | demo | alter | ab3ffdd5_f25c_11ea_bab4_0242c0a8b007 | online | 2020-09-09 05:24:33 | 2020-09-09 05:24:34 | complete |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+
The syntax for tracking migrations is:
vtctlclient OnlineDDL [-json] <keyspace> show <migration_id|all|recent|queued|ready|running|complete|failed|cancelled>
Showing migration logs
gh-ost and pt-osc tools generate logs files, which are retrievable for 24 hours after migration completion/failure.
Via VTGate/SQL
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 261355426d8fc31b590733ca8ff8e79012103c182021-07-19 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-startupok2021-07-19 07:59:23 INFO inspector connection validated on ip-REDACTED:171002021-07-19 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:171002021-07-19 07:59:23 INFO Restarting replication on ip-REDACTED:17100 to make sure binlog settings apply to replication thread2021-07-19 07:59:23 INFO Inspector initiated on ip-REDACTED:17100, version 5.7.30-log2021-07-19 07:59:23 INFO Table found. Engine=InnoDB...
Launching a migration
Migrations submitted with --postpone-launch remain queued or ready until told to launch. The user may launch a specific migration or they may launch all postponed migrations:
Via VTGate/SQL
mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' launch;Query OK, 1 row affected (0.01 sec)
or
mysql> alter vitess_migration launch all;Query OK, 1 row affected (0.01 sec)
Via vtctlclient/ApplySchema
Launch a specific migration:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration '9e8a9249_3976_11ed_9442_0a43f95f28a3' launch" commerce
Or launch a specific migration on a specific shard:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration '9e8a9249_3976_11ed_9442_0a43f95f28a3' launch vitess_shards '-40,40-80'" commerce
Or launch all:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration launch all" commerce
Completing a migration
Migrations submitted with --postpone-completion remain ready or running until told to complete. The user may complete a specific migration or they may complete all postponed migrations:
Via VTGate/SQL
mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' complete;Query OK, 1 row affected (0.01 sec)
or
mysql> alter vitess_migration complete all;Query OK, 1 row affected (0.01 sec)
Via vtctlclient/ApplySchema
Complete a specific migration:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration '9e8a9249_3976_11ed_9442_0a43f95f28a3' complete" commerce
Or complete all:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration complete all" commerce
Cancelling a migration
The user may cancel a migration, as follows:
- If the migration hasn’t started yet (it is
queuedorready), then it transitions intocancelledstate and doesn’t get executed. - If the migration is
running, then it is forcibly interrupted. The migration transitions tocancelledstate. - In all other cases, cancelling a migration has no effect.
Via VTGate/SQL
Examples for a single shard cluster:
id: 28migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: cordermigration_statement: alter table corder add column handler_id int not nullstrategy: gh-ostoptions:added_timestamp: 2021-03-25 14:50:27requested_timestamp: 2021-03-25 14:50:24ready_timestamp: 2021-03-25 14:50:31started_timestamp: 2021-03-25 14:50:32liveness_timestamp: 2021-03-25 14:50:32completed_timestamp: NULLcleanup_timestamp: NULLmigration_status: running...mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' cancel;Query OK, 1 row affected (0.01 sec)mysql> show vitess_migrations like 'aa89f255_8d68_11eb_815f_f875a4d24e90' \G*************************** 1. row ***************************id: 28migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: cordermigration_statement: alter table corder add column handler_id int not nullstrategy: gh-ostoptions: --throttle-flag-file=/tmp/throttle.flagadded_timestamp: 2021-03-25 14:50:27requested_timestamp: 2021-03-25 14:50:24ready_timestamp: 2021-03-25 14:50:31started_timestamp: 2021-03-25 14:50:32liveness_timestamp: 2021-03-25 14:50:32completed_timestamp: NULLcleanup_timestamp: NULLmigration_status: cancelled...
alter vitess_migration ... canceltakes exactly one migration’s UUID.alter vitess_migration ... cancelresponds with number of affected migrations.
Via vtctlclient/ApplySchema
Examples for a 4-shard cluster:
vtctlclient OnlineDDL <keyspace> cancel <migration_id>
Example:
$ vtctlclient OnlineDDL commerce show 2201058f_f266_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000301 | 80-c0 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | running || test-0000000101 | -40 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | running || test-0000000401 | c0- | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | running || test-0000000201 | 40-80 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | running |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce cancel 2201058f_f266_11ea_bab4_0242c0a8b007$ vtctlclient OnlineDDL commerce show 2201058f_f266_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000401 | c0- | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | cancelled || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | cancelled || test-0000000201 | 40-80 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | cancelled || test-0000000101 | -40 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | cancelled |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+
Cancelling all keyspace migrations
The user may cancel all migrations in a keyspace. A migration is cancellable if it is in queued, ready or running states, as described previously. It is a high impact operation and should be used with care.
Via VTGate/SQL
Examples for a single shard cluster:
mysql> alter vitess_migration cancel all;Query OK, 1 row affected (0.02 sec)
Via vtctlclient/ApplySchema
Examples for a 4-shard cluster:
$ vtctlclient -- ApplySchema --sql "alter vitess_migration cancel all" commerce
Also available via vtctlclient OnlineDDL command:
vtctlclient OnlineDDL <keyspace> cancel-all
Example:
$ vtctlclient OnlineDDL commerce show all+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+| zone1-0000000100 | 0 | vt_commerce | corder | 2c581994_353a_11eb_8b72_f875a4d24e90 | online | | | queued || zone1-0000000100 | 0 | vt_commerce | corder | 2c6420c9_353a_11eb_8b72_f875a4d24e90 | online | | | queued || zone1-0000000100 | 0 | vt_commerce | corder | 2c7040df_353a_11eb_8b72_f875a4d24e90 | online | | | queued || zone1-0000000100 | 0 | vt_commerce | corder | 2c7c0572_353a_11eb_8b72_f875a4d24e90 | online | | | queued || zone1-0000000100 | 0 | vt_commerce | corder | 2c87f7cd_353a_11eb_8b72_f875a4d24e90 | online | | | queued |+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce cancel-all$ vtctlclient OnlineDDL commerce show all+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+| zone1-0000000100 | 0 | vt_commerce | corder | 2c581994_353a_11eb_8b72_f875a4d24e90 | online | | | cancelled || zone1-0000000100 | 0 | vt_commerce | corder | 2c6420c9_353a_11eb_8b72_f875a4d24e90 | online | | | cancelled || zone1-0000000100 | 0 | vt_commerce | corder | 2c7040df_353a_11eb_8b72_f875a4d24e90 | online | | | cancelled || zone1-0000000100 | 0 | vt_commerce | corder | 2c7c0572_353a_11eb_8b72_f875a4d24e90 | online | | | cancelled || zone1-0000000100 | 0 | vt_commerce | corder | 2c87f7cd_353a_11eb_8b72_f875a4d24e90 | online | | | cancelled |+------------------+-------+--------------+-------------+--------------------------------------+----------+-------------------+---------------------+------------------+
Retrying a migration
The user may retry running a migration. If the migration is in failed or in cancelled state, Vitess will re-run the migration, with exact same arguments as previously intended. If the migration is in any other state, retry does nothing.
It is not possible to retry a migration with different options. e.g. if the user initially runs ALTER TABLE demo MODIFY id BIGINT with @@ddl_strategy='gh-ost --max-load Threads_running=200' and the migration fails, retrying it will use exact same options. It is not possible to retry with @@ddl_strategy='gh-ost --max-load Threads_running=500'.
Via VTGate/SQL
Examples for a single shard cluster:
*************************** 1. row ***************************id: 28migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: cordermigration_statement: alter table corder add column handler_id int not nullstrategy: gh-ostoptions: --throttle-flag-file=/tmp/throttle.flagadded_timestamp: 2021-03-25 14:50:27requested_timestamp: 2021-03-25 14:50:24ready_timestamp: 2021-03-25 14:56:22started_timestamp: 2021-03-25 14:56:22liveness_timestamp: 2021-03-25 14:56:22completed_timestamp: NULLcleanup_timestamp: NULLmigration_status: failed...mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' retry;Query OK, 1 row affected (0.00 sec)mysql> show vitess_migrations like 'aa89f255_8d68_11eb_815f_f875a4d24e90' \G*************************** 1. row ***************************id: 28migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90keyspace: commerceshard: 0mysql_schema: vt_commercemysql_table: cordermigration_statement: alter table corder add column handler_id int not nullstrategy: gh-ostoptions: --throttle-flag-file=/tmp/throttle.flagadded_timestamp: 2021-03-25 14:50:27requested_timestamp: 2021-03-25 14:50:24ready_timestamp: 2021-03-25 14:56:42started_timestamp: 2021-03-25 14:56:42liveness_timestamp: 2021-03-25 14:56:42completed_timestamp: NULLcleanup_timestamp: NULLmigration_status: running...
alter vitess_migration ... retrytakes exactly one migration’s UUID.alter vitess_migration ... retryresponds with number of affected migrations.
Via vtctlclient/ApplySchema
$ vtctlclient -- ApplySchema --sql "alter vitess_migration '2201058f_f266_11ea_bab4_0242c0a8b007' retry" commerce
Also available via vtctlclient OnlineDDL command:
Examples for a 4-shard cluster:
$ vtctlclient OnlineDDL commerce show 2201058f_f266_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000401 | c0- | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | failed || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | failed || test-0000000201 | 40-80 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | failed || test-0000000101 | -40 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:32:31 | | failed |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce retry 2201058f_f266_11ea_bab4_0242c0a8b007$ vtctlclient OnlineDDL commerce show 2201058f_f266_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+-------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+-------------------+---------------------+------------------+| test-0000000201 | 40-80 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | | | queued || test-0000000101 | -40 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | | | queued || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | | | queued || test-0000000401 | c0- | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | | | queued |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+-------------------+---------------------+------------------+$ vtctlclient OnlineDDL commerce show 2201058f_f266_11ea_bab4_0242c0a8b007+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| Tablet | shard | mysql_schema | mysql_table | ddl_action | migration_uuid | strategy | started_timestamp | completed_timestamp | migration_status |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+| test-0000000101 | -40 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:37:33 | | running || test-0000000401 | c0- | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:37:33 | | running || test-0000000201 | 40-80 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:37:33 | | running || test-0000000301 | 80-c0 | vt_commerce | demo | alter | 2201058f_f266_11ea_bab4_0242c0a8b007 | online | 2020-09-09 06:37:33 | | running |+-----------------+-------+--------------+-------------+------------+--------------------------------------+----------+---------------------+---------------------+------------------+
Cleaning migration artifacts
Migrations yield artifacts: these are leftover tables, such as the ghost or shadow tables in an ALTER DDL. These tables are audited and collected as part of table lifecycle.
The artifacts are essential to Reverting a migration, and are kept intact for a while before destroyed.
However, the artifacts also consume disk space. If the user is convinced they will not need the artifacts, they may explicitly request that the artifacts are dropped sooner.
Once cleanup is requested, the migration cannot be reverted.
The artifact tables are not purged immediately. Rather, they are sent for processing into the lifecycle mechanism.
Via VTGate/SQL
Per migration, request artifact cleanup via:
mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' cleanup;Query OK, 1 row affected (0.00 sec)
Reverting a migration
Vitess offers lossless revert for online schema migrations: the user may regret a table migration after completion, and roll back the table’s schema to previous state without loss of data. See Revertible Migrations.
Via VTGate/SQL
Examples for a single shard cluster:
mysql> show create table corder\GCreate Table: CREATE TABLE `corder` (`order_id` bigint(20) NOT NULL AUTO_INCREMENT,`customer_id` bigint(20) DEFAULT NULL,`sku` varbinary(128) DEFAULT NULL,`price` bigint(20) DEFAULT NULL,`ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,PRIMARY KEY (`order_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.01 sec)mysql> alter table corder drop column ts, add key customer_idx(customer_id);+--------------------------------------+| uuid |+--------------------------------------+| 1a689113_8d77_11eb_815f_f875a4d24e90 |+--------------------------------------+mysql> show create table corder\GCreate Table: CREATE TABLE `corder` (`order_id` bigint(20) NOT NULL AUTO_INCREMENT,`customer_id` bigint(20) DEFAULT NULL,`sku` varbinary(128) DEFAULT NULL,`price` bigint(20) DEFAULT NULL,PRIMARY KEY (`order_id`),KEY `customer_idx` (`customer_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.00 sec)mysql> revert vitess_migration '1a689113_8d77_11eb_815f_f875a4d24e90';+--------------------------------------+| uuid |+--------------------------------------+| a02e6612_8d79_11eb_815f_f875a4d24e90 |+--------------------------------------+mysql> show create table corder\GCreate Table: CREATE TABLE `corder` (`order_id` bigint(20) NOT NULL AUTO_INCREMENT,`customer_id` bigint(20) DEFAULT NULL,`sku` varbinary(128) DEFAULT NULL,`price` bigint(20) DEFAULT NULL,`ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,PRIMARY KEY (`order_id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8
- A
revertis its own migration, hence has its own UUID
Via vtctlclient/ApplySchema
$ vtctlclient -- ApplySchema --ddl_strategy "vitess" --sql "revert vitess_migration '1a689113_8d77_11eb_815f_f875a4d24e90'" commerce
Controlling throttling
Managed migrations use the tablet throttler to ensure a sustainable impact to the MySQL servers and replication stream. Normally, the user doesn’t need to get involved, as the throttler auto-identifies load scenarios, and pushes back on migration progress. However, Vitess makes available these commands for additional control over migration throttling:
alter vitess_migration '<uuid>' throttle [expire '<duration>'] [ratio <ratio>];alter vitess_migration throttle all [expire '<duration>'] [ratio <ratio>];alter vitess_migration '<uuid>' unthrottle;alter vitess_migration unthrottle all;show vitess_throttled_apps;
Note: the tablet throttler must be enabled for these command to run.
Throttling a migration
To fully throttle a migration, run:
mysql> alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' throttle;Query OK, 1 row affected (0.00 sec)
From this point on, the migration will not make row copy progress and will not apply binary logs. By default, this command does not expire, and it takes an explicit unthrottle command to resume migration progress. Because MySQL binary logs are rotated, a migration may only survive a full throttling up to the point where the binary log it last processed is purged.
You may supply either or both these options: expire, ratio:
alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' throttle expire '2h'will fully throttle the migration for the next2hours, after which the migration resumes normal work. You may specify these units:s(seconds),m(minutes),h(hours) or combinations. Example values:90s,30m,1h,1h30m, etc.alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' throttle ratio 0.7will partially throttle the migration. This instructs the throttler to reject, on average,7migration throttling check requests out of10. Any value between0(no throttling at all) and1.0(fully throttled) are allowed. This is a fine tune way to slow down a migration.
Throttling all migrations
It’s likely that you will want to throttle migrations in general, and not a specific migration. Use:
alter vitess_migration throttle all;to fully throttle any and all migrations from this point onalter vitess_migration throttle all expire '90m';to fully throttle any and all migrations from this point on and for the next90minutes.alter vitess_migration throttle all ratio 0.8;to severely slow down all migrations from this point on (4 out of 5 migrations requests to the throttler are denied)alter vitess_migration throttle all duration '10m' ratio 0.2;to lightly slow down all migrations from this point on (1 out of 5 migrations requests to the throttler are denied) for the next10minutes.
Unthrottling
Use:
alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' unthrottle;to allow the specified migration to resume working as normalalter vitess_migration unthrottle all;to unthrottle all migrations.
Note that this does not disable throttling altogether. If, for example, replication lag grows on replicas, the throttler may still throttle the migration until replication is caught up. Unthrottling only cancels an explicit throttling request as described above.
Showing throttled apps
The command show vitess_throttled_apps; is a general purpose throttler command, and shows all apps for which there are throttling rules. It will list any specific or general migration throttling status.
