This is used in EE for the storage migration, and we want to use this
in CE as well to be able to migrate projects to hashed_storage.

This is a composite index on (target_project_id, merge_commit_sha, id)
that allows queries such as the following to use a full backwards index
scan:

    SELECT "merge_requests".*
    FROM "merge_requests"
    WHERE "merge_requests"."deleted_at" IS NULL
    AND "merge_requests"."target_project_id" = 13083
    AND "merge_requests"."merge_commit_sha" = 'e80a893f'
    ORDER BY "merge_requests"."id" DESC
    LIMIT 1;

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/38507

Migration 20170919211300_remove_temporary_ci_builds_index.rb created a
temporary partial index and tried to drop it at the end of the
migration. In some circumstances apparently it failed to drop the
index and it ended up in our schema.rb.

This accidentally failed to fail due to a bug in the regular
expression for partial indexes which caused the index creation in
schema.rb to be ignored. Now that that's fixed we could be
resurrecting this zombie index from the past in some but not all
databases.

Add a migration to drop this index if it's present to reconcile this
discrepancy.

This removes the need for a default scope that adds a "WHERE project_id
= X" clause. This commit also includes an additional index for
Environment#last_deployment, ensuring this query uses just an index scan
instead of also applying a Filter.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/36877

This index is required to allow fast retrieval of recent push events
without merge requests. Without this index in place the query would
lead to PostgreSQL scanning over 150 000 index entries all the time,
easily taking up between 200 and 500 milliseconds. This index
reduces the time spent in this process to around 40 milliseconds on
GitLab.com.

This reverts merge request !14148

Revert "Merge branch '35012-navigation-add-option-to-change-navigation-color-palette' into 'master'"

This reverts merge request !13619

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This finishes the procedure for migrating events from the old format
into the new format. Code no longer uses the old setup and the database
tables used during the migration process are swapped, with the old table
being dropped.

While the database migration can be reversed this will 1) take a lot of
time as data has to be coped around 2) won't restore data in the
"events.data" column as we have no way of restoring this.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/37241

To avoid having to implement legacy code handling for the obsolete
`verified_signature` attribute and to avoid any race conditions during
the zero-downtime-deployment we do the following:

1. Destroy all records
2. Migration: Use add_column_with_default to add the new attribute and
   update the verification_status values on records created between 1.
   and 2.
3. Deploy the new code
4. Post migration: Destroy all records

Like this we make sure that at no point there is a record with a `nil`
value for the new `verification_status` attribute.

Remove access_level index from runner. Add protected on ci_pipelines. Add protected index on ci_builds.

Re-organize schema. Drop protected from runner. Add access_level to runner. Drop protected from pipeline. Add protected to ci_bilds.

Solution 1. Persists protected(ref) flag on ci_pipelines table. builds_for_shared_runner and builds_for_specific_runner read the flag instead of executing protected_for? one by one.