Update reindexing documentation

Ref: #474639 (closed)

What does this MR do and why?

This MR updates our reindexing documentation.

Click to expand

➜  gitlab git:(morefice/update-reindexing-documentation) ✗ bin/rails runner 'ApplicationSetting.current.update!(database_reindexing: { reindexing_minimum_index_size: 100.bytes })'
DEPRECATION WARNING: Support for Rails versions < 7.1 is deprecated and will be removed from ViewComponent 4.0.0 (ViewComponent v4 will remove support for Rails versions < 7.1 no earlier than April 1, 2025) (called from <main> at /Users/morefice/code/gitlab-development-kit/gitlab/config/environment.rb:7)
➜  gitlab git:(morefice/update-reindexing-documentation) ✗ bin/rake gitlab:db:reindex
DEPRECATION WARNING: Support for Rails versions < 7.1 is deprecated and will be removed from ViewComponent 4.0.0 (ViewComponent v4 will remove support for Rails versions < 7.1 no earlier than April 1, 2025) (called from <main> at /Users/morefice/code/gitlab-development-kit/gitlab/config/environment.rb:7)
W, [2025-04-15T09:39:41.447288 #16954]  WARN -- : Query fetched 5559 Gitlab::Database::PostgresIndex records: SELECT "postgres_indexes".* FROM "postgres_indexes" WHERE "postgres_indexes"."exclusion" = FALSE AND "postgres_indexes"."expression" = FALSE AND "postgres_indexes"."type" IN ('btree', 'gist') AND (name !~ '\_cc(new|old)[0-9]*$') AND (NOT EXISTS (SELECT "postgres_reindex_actions".* FROM "postgres_reindex_actions" WHERE "postgres_reindex_actions"."state" = 1 AND (action_end > '2025-04-05 07:39:41.187463') AND (index_identifier = identifier))) AND (NOT EXISTS (SELECT 1 FROM "postgres_partitioned_tables" WHERE "postgres_partitioned_tables"."schema" = "postgres_indexes"."schema" AND "postgres_partitioned_tables"."name" = "postgres_indexes"."tablename")) AND (ondisk_size_bytes >= 100) /*application:web,db_config_database:gitlabhq_development,db_config_name:main,line:/lib/gitlab/database/reindexing/index_selection.rb:32:in `sort_by'*/;SELECT c.relname FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace WHERE n.nspname = ANY (current_schemas(false)) AND c.relkind IN ('r','v','m','p','f')