Fix batched migrations using legacy job arguments

What does this MR do?

Some of the PK conversions, using the new batched background migrations, were released first for GitLab.com, and later for self-managed. Meanwhile we changed the format we use for batched_background_migrations.job_arguments. This MR updates the records using the legacy format to what we currently use.

Database migrations

When migrations with both legacy and current format exist

gitlabhq_development=# select id, job_class_name, table_name, column_name, job_arguments from batched_background_migrations where table_name in ('events', 'push_event_payloads') order by id asc;
 id |            job_class_name             |     table_name      | column_name |                 job_arguments                  
----+---------------------------------------+---------------------+-------------+------------------------------------------------
 41 | CopyColumnUsingBackgroundMigrationJob | events              | id          | ["id", "id_convert_to_bigint"]
 42 | CopyColumnUsingBackgroundMigrationJob | push_event_payloads | event_id    | ["event_id", "event_id_convert_to_bigint"]
 51 | CopyColumnUsingBackgroundMigrationJob | events              | id          | [["id"], ["id_convert_to_bigint"]]
 52 | CopyColumnUsingBackgroundMigrationJob | push_event_payloads | event_id    | [["event_id"], ["event_id_convert_to_bigint"]]
(4 rows)

Up

$ bundle exec rails db:migrate:up VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrating ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrated (0.0090s) 

Down

$ bundle exec rails db:migrate:down VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverting ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverted (0.0000s) 

When migrations with only the current format exist

gitlabhq_development=# select id, job_class_name, table_name, column_name, job_arguments from batched_background_migrations where table_name in ('events', 'push_event_payloads') order by id asc;
 id |            job_class_name             |     table_name      | column_name |                 job_arguments                  
----+---------------------------------------+---------------------+-------------+------------------------------------------------
 51 | CopyColumnUsingBackgroundMigrationJob | events              | id          | [["id"], ["id_convert_to_bigint"]]
 52 | CopyColumnUsingBackgroundMigrationJob | push_event_payloads | event_id    | [["event_id"], ["event_id_convert_to_bigint"]]
(2 rows)

Up

$ bundle exec rails db:migrate:up VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrating ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrated (0.0082s) 

Down

$ bundle exec rails db:migrate:down VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverting ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverted (0.0000s) 

When migrations with only the legacy format exist

gitlabhq_development=# select id, job_class_name, table_name, column_name, job_arguments from batched_background_migrations where table_name in ('events', 'push_event_payloads') order by id asc;
 id |            job_class_name             |     table_name      | column_name |               job_arguments                
----+---------------------------------------+---------------------+-------------+--------------------------------------------
 41 | CopyColumnUsingBackgroundMigrationJob | events              | id          | ["id", "id_convert_to_bigint"]
 42 | CopyColumnUsingBackgroundMigrationJob | push_event_payloads | event_id    | ["event_id", "event_id_convert_to_bigint"]
(2 rows)

Up

$ bundle exec rails db:migrate:up VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrating ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: migrated (0.0081s) 

The records after being migrated:

gitlabhq_development=# select id, job_class_name, table_name, column_name, job_arguments from batched_background_migrations where table_name in ('events', 'push_event_payloads') order by id asc;
 id |            job_class_name             |     table_name      | column_name |                 job_arguments                  
----+---------------------------------------+---------------------+-------------+------------------------------------------------
 41 | CopyColumnUsingBackgroundMigrationJob | events              | id          | [["id"], ["id_convert_to_bigint"]]
 42 | CopyColumnUsingBackgroundMigrationJob | push_event_payloads | event_id    | [["event_id"], ["event_id_convert_to_bigint"]]
(2 rows

Down

$ bundle exec rails db:migrate:down VERSION=20210615234935
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverting ========
== 20210615234935 FixBatchedMigrationsOldFormatJobArguments: reverted (0.0000s) 

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

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• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #331815 (closed)