Applying, auditing, and controlling Online DDL

Vitess provides two interfaces to interacting with Online DDL:

  • SQL commands, via VTGate
  • Command line interface, via vtctl

Supported interactions are:

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_strategy behaves like a MySQL session variable, though is only recognized by VTGate. Setting @@ddl_strategy only 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_strategy to different value.
  • If you run vtgate without --ddl_strategy, then @@ddl_strategy defaults to 'direct', which implies schema migrations are synchronous. You will need to set @@ddl_strategy='gh-ost' to run followup ALTER TABLE statements via gh-ost.
  • If you run vtgate --ddl_strategy "gh-ost", then @@ddl_strategy defaults to 'gh-ost' in each new session. Any ALTER TABLE will run via gh-ost. You may set @@ddl_strategy='pt-osc' to make migrations run through pt-online-schema-change, or set @@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" commerce
a2994c92_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;" commerce
3091ef2a_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 a ApplySchema command 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, via SHOW VITESS_MIGRATIONS LIKE 'the-context'. It is visible in SHOW VITESS_MIGRATIONS ... output as the migration_context column.
  • --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 to true.

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, complete or failed migrations
  • 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: 23
     migration_uuid: bf4598ab_8d55_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: corder
migration_statement: alter table corder add column ts timestamp not null default current_timestamp()
           strategy: vitess
            options: 
    added_timestamp: 2021-03-25 12:35:01
requested_timestamp: 2021-03-25 12:34:58
    ready_timestamp: 2021-03-25 12:35:04
  started_timestamp: 2021-03-25 12:35:04
 liveness_timestamp: 2021-03-25 12:35:06
completed_timestamp: 2021-03-25 12:35:06
  cleanup_timestamp: NULL
   migration_status: complete
           log_path: 
          artifacts: _bf4598ab_8d55_11eb_815f_f875a4d24e90_20210325123504_vrepl,
            retries: 0
             tablet: zone1-0000000100
     tablet_failure: 0
           progress: 100
  migration_context: vtgate:a8352418-8d55-11eb-815f-f875a4d24e90
         ddl_action: alter
            message: 
        eta_seconds: 0

mysql> show vitess_migrations like 'complete' \G
...
*************************** 21. row ***************************
                 id: 24
     migration_uuid: 6848c1a4_8d57_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: customer
migration_statement: drop table customer
           strategy: vitess
            options: 
    added_timestamp: 2021-03-25 12:46:53
requested_timestamp: 2021-03-25 12:46:51
    ready_timestamp: 2021-03-25 12:46:57
  started_timestamp: 2021-03-25 12:46:57
 liveness_timestamp: 2021-03-25 12:46:57
completed_timestamp: 2021-03-25 12:46:57
  cleanup_timestamp: NULL
   migration_status: complete
           log_path: 
          artifacts: _vt_HOLD_6848c1a48d5711eb815ff875a4d24e90_20210326104657,
            retries: 0
             tablet: zone1-0000000100
     tablet_failure: 0
           progress: 100
  migration_context: vtgate:a8352418-8d55-11eb-815f-f875a4d24e90
         ddl_action: drop
            message: 
        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_migrations shows the entire history of migrations.
  • show vitess_migrations like ... filters migrations by migration_uuid, or migration_context, or migration_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 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
...

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 queued or ready), then it transitions into cancelled state and doesn't get executed.
  • If the migration is running, then it is forcibly interrupted. The migration transitions to cancelled state.
  • In all other cases, cancelling a migration has no effect.

Via VTGate/SQL #

Examples for a single shard cluster:

                 id: 28
     migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: corder
migration_statement: alter table corder add column handler_id int not null
           strategy: gh-ost
            options: 
    added_timestamp: 2021-03-25 14:50:27
requested_timestamp: 2021-03-25 14:50:24
    ready_timestamp: 2021-03-25 14:50:31
  started_timestamp: 2021-03-25 14:50:32
 liveness_timestamp: 2021-03-25 14:50:32
completed_timestamp: NULL
  cleanup_timestamp: NULL
   migration_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: 28
     migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: corder
migration_statement: alter table corder add column handler_id int not null
           strategy: gh-ost
            options: --throttle-flag-file=/tmp/throttle.flag
    added_timestamp: 2021-03-25 14:50:27
requested_timestamp: 2021-03-25 14:50:24
    ready_timestamp: 2021-03-25 14:50:31
  started_timestamp: 2021-03-25 14:50:32
 liveness_timestamp: 2021-03-25 14:50:32
completed_timestamp: NULL
  cleanup_timestamp: NULL
   migration_status: cancelled
...
  • alter vitess_migration ... cancel takes exactly one migration's UUID.
  • alter vitess_migration ... cancel responds 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: 28
     migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: corder
migration_statement: alter table corder add column handler_id int not null
           strategy: gh-ost
            options: --throttle-flag-file=/tmp/throttle.flag
    added_timestamp: 2021-03-25 14:50:27
requested_timestamp: 2021-03-25 14:50:24
    ready_timestamp: 2021-03-25 14:56:22
  started_timestamp: 2021-03-25 14:56:22
 liveness_timestamp: 2021-03-25 14:56:22
completed_timestamp: NULL
  cleanup_timestamp: NULL
   migration_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: 28
     migration_uuid: aa89f255_8d68_11eb_815f_f875a4d24e90
           keyspace: commerce
              shard: 0
       mysql_schema: vt_commerce
        mysql_table: corder
migration_statement: alter table corder add column handler_id int not null
           strategy: gh-ost
            options: --throttle-flag-file=/tmp/throttle.flag
    added_timestamp: 2021-03-25 14:50:27
requested_timestamp: 2021-03-25 14:50:24
    ready_timestamp: 2021-03-25 14:56:42
  started_timestamp: 2021-03-25 14:56:42
 liveness_timestamp: 2021-03-25 14:56:42
completed_timestamp: NULL
  cleanup_timestamp: NULL
   migration_status: running
...
  • alter vitess_migration ... retry takes exactly one migration's UUID.
  • alter vitess_migration ... retry responds 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\G

Create 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
1 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\G

Create 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=utf8
1 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\G

Create 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 revert is 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 next 2 hours, 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 0.7 will partially throttle the migration. This instructs the throttler to reject, on average, 7 migration throttling check requests out of 10. Any value between 0 (no throttling at all) and 1.0 (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 on
  • alter vitess_migration throttle all expire '90m'; to fully throttle any and all migrations from this point on and for the next 90 minutes.
  • 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 next 10 minutes.

Unthrottling #

Use:

  • alter vitess_migration 'aa89f255_8d68_11eb_815f_f875a4d24e90' unthrottle; to allow the specified migration to resume working as normal
  • alter 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.

Applying, auditing, and controlling Online DDL