Remove `if Gitlab::Database.postgresql?` branches

GitLab supports PostgreSQL only since https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/29790.

Follows up https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/29608,
https://gitlab.com/gitlab-org/gitlab/merge_requests/14645,
https://gitlab.com/gitlab-org/gitlab/commit/988dc80585c6e52970e94f22dff6bc1e4c786e9e,
https://gitlab.com/gitlab-org/gitlab/merge_requests/14239,
https://gitlab.com/gitlab-org/gitlab/merge_requests/20319

/cc @nick.thomas

db/migrate/20180215181245_users_name_lower_index.rb

@@ -11,15 +11,11 @@ class UsersNameLowerIndex < ActiveRecord::Migration[4.2]
   disable_ddl_transaction!
 
   def up
-    return unless Gitlab::Database.postgresql?
-
     # On GitLab.com this produces an index with a size of roughly 60 MB.
     execute "CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON users (LOWER(name))"
   end
 
   def down
-    return unless Gitlab::Database.postgresql?
-
     execute "DROP INDEX CONCURRENTLY IF EXISTS #{INDEX_NAME}"
   end
 end

db/migrate/20180309121820_reschedule_commits_count_for_merge_request_diff.rb

@@ -18,7 +18,7 @@ class RescheduleCommitsCountForMergeRequestDiff < ActiveRecord::Migration[4.2]
   def up
     say 'Populating the MergeRequestDiff `commits_count` (reschedule)'
 
-    execute("SET statement_timeout TO '60s'") if Gitlab::Database.postgresql?
+    execute("SET statement_timeout TO '60s'")
 
     MergeRequestDiff.where(commits_count: nil).each_batch(of: BATCH_SIZE) do |relation, index|
       start_id, end_id = relation.pluck('MIN(id), MAX(id)').first

db/migrate/20180504195842_project_name_lower_index.rb

@@ -11,16 +11,12 @@ class ProjectNameLowerIndex < ActiveRecord::Migration[4.2]
   disable_ddl_transaction!
 
   def up
-    return unless Gitlab::Database.postgresql?
-
     disable_statement_timeout do
       execute "CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON projects (LOWER(name))"
     end
   end
 
   def down
-    return unless Gitlab::Database.postgresql?
-
     disable_statement_timeout do
       execute "DROP INDEX CONCURRENTLY IF EXISTS #{INDEX_NAME}"
     end

db/migrate/20180517082340_add_not_null_constraints_to_project_authorizations.rb

@@ -5,34 +5,20 @@ class AddNotNullConstraintsToProjectAuthorizations < ActiveRecord::Migration[4.2
   DOWNTIME = false
 
   def up
-    if Gitlab::Database.postgresql?
-      # One-pass version for PostgreSQL
     execute <<~SQL
       ALTER TABLE project_authorizations
         ALTER COLUMN user_id SET NOT NULL,
         ALTER COLUMN project_id SET NOT NULL,
         ALTER COLUMN access_level SET NOT NULL
     SQL
-    else
-      change_column_null :project_authorizations, :user_id, false
-      change_column_null :project_authorizations, :project_id, false
-      change_column_null :project_authorizations, :access_level, false
-    end
   end
 
   def down
-    if Gitlab::Database.postgresql?
-      # One-pass version for PostgreSQL
     execute <<~SQL
       ALTER TABLE project_authorizations
         ALTER COLUMN user_id DROP NOT NULL,
         ALTER COLUMN project_id DROP NOT NULL,
         ALTER COLUMN access_level DROP NOT NULL
     SQL
-    else
-      change_column_null :project_authorizations, :user_id, true
-      change_column_null :project_authorizations, :project_id, true
-      change_column_null :project_authorizations, :access_level, true
-    end
   end
 end

db/migrate/20190402150158_backport_enterprise_schema.rb

@@ -464,15 +464,12 @@ class BackportEnterpriseSchema < ActiveRecord::Migration[5.0]
   end
 
   def update_environments
-    return unless Gitlab::Database.postgresql?
     return if index_exists?(:environments, :name, name: 'index_environments_on_name_varchar_pattern_ops')
 
     execute('CREATE INDEX CONCURRENTLY index_environments_on_name_varchar_pattern_ops ON environments (name varchar_pattern_ops);')
   end
 
   def revert_environments
-    return unless Gitlab::Database.postgresql?
-
     remove_concurrent_index_by_name(
       :environments,
       'index_environments_on_name_varchar_pattern_ops'

db/optional_migrations/composite_primary_keys.rb

@@ -27,8 +27,6 @@ class CompositePrimaryKeysMigration < ActiveRecord::Migration[4.2]
   disable_ddl_transaction!
 
   def up
-    return unless Gitlab::Database.postgresql?
-
     disable_statement_timeout do
       TABLES.each do |index|
         add_primary_key(index)
@@ -37,8 +35,6 @@ class CompositePrimaryKeysMigration < ActiveRecord::Migration[4.2]
   end
 
   def down
-    return unless Gitlab::Database.postgresql?
-
     disable_statement_timeout do
       TABLES.each do |index|
         remove_primary_key(index)

db/post_migrate/20180305100050_remove_permanent_from_redirect_routes.rb

@@ -14,12 +14,10 @@ class RemovePermanentFromRedirectRoutes < ActiveRecord::Migration[4.2]
     # These indexes were created on Postgres only in:
     # ReworkRedirectRoutesIndexes:
     # https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/16211
-    if Gitlab::Database.postgresql?
     disable_statement_timeout do
       execute "DROP INDEX CONCURRENTLY IF EXISTS #{INDEX_NAME_PERM};"
       execute "DROP INDEX CONCURRENTLY IF EXISTS #{INDEX_NAME_TEMP};"
     end
-    end
 
     remove_column(:redirect_routes, :permanent)
   end
@@ -27,11 +25,9 @@ class RemovePermanentFromRedirectRoutes < ActiveRecord::Migration[4.2]
   def down
     add_column(:redirect_routes, :permanent, :boolean)
 
-    if Gitlab::Database.postgresql?
     disable_statement_timeout do
       execute("CREATE INDEX CONCURRENTLY #{INDEX_NAME_PERM} ON redirect_routes (lower(path) varchar_pattern_ops) where (permanent);")
       execute("CREATE INDEX CONCURRENTLY #{INDEX_NAME_TEMP} ON redirect_routes (lower(path) varchar_pattern_ops) where (not permanent or permanent is null) ;")
     end
   end
-  end
 end

db/post_migrate/20180306164012_add_path_index_to_redirect_routes.rb

@@ -16,8 +16,6 @@ class AddPathIndexToRedirectRoutes < ActiveRecord::Migration[4.2]
   # This same index is also added in the `ReworkRedirectRoutesIndexes` so this
   # is a no-op in most cases.
   def up
-    return unless Gitlab::Database.postgresql?
-
     disable_statement_timeout do
       unless index_exists_by_name?(:redirect_routes, INDEX_NAME)
         execute("CREATE UNIQUE INDEX CONCURRENTLY #{INDEX_NAME} ON redirect_routes (lower(path) varchar_pattern_ops);")

db/post_migrate/20180706223200_populate_site_statistics.rb

@@ -7,13 +7,13 @@ class PopulateSiteStatistics < ActiveRecord::Migration[4.2]
 
   def up
     transaction do
-      execute('SET LOCAL statement_timeout TO 0') if Gitlab::Database.postgresql? # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
+      execute('SET LOCAL statement_timeout TO 0') # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
 
       execute("UPDATE site_statistics SET repositories_count = (SELECT COUNT(*) FROM projects)")
     end
 
     transaction do
-      execute('SET LOCAL statement_timeout TO 0') if Gitlab::Database.postgresql? # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
+      execute('SET LOCAL statement_timeout TO 0') # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
 
       execute("UPDATE site_statistics SET wikis_count = (SELECT COUNT(*) FROM project_features WHERE wiki_access_level != 0)")
     end

db/post_migrate/20180809195358_migrate_null_wiki_access_levels.rb

@@ -20,7 +20,7 @@ class MigrateNullWikiAccessLevels < ActiveRecord::Migration[4.2]
 
     # We need to re-count wikis as previous attempt was not considering the NULLs.
     transaction do
-      execute('SET LOCAL statement_timeout TO 0') if Gitlab::Database.postgresql? # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
+      execute('SET LOCAL statement_timeout TO 0') # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
 
       execute("UPDATE site_statistics SET wikis_count = (SELECT COUNT(*) FROM project_features WHERE wiki_access_level != 0)")
     end

db/post_migrate/20180826111825_recalculate_site_statistics.rb

@@ -9,13 +9,13 @@ class RecalculateSiteStatistics < ActiveRecord::Migration[4.2]
 
   def up
     transaction do
-      execute('SET LOCAL statement_timeout TO 0') if Gitlab::Database.postgresql? # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
+      execute('SET LOCAL statement_timeout TO 0') # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
 
       execute("UPDATE site_statistics SET repositories_count = (SELECT COUNT(*) FROM projects)")
     end
 
     transaction do
-      execute('SET LOCAL statement_timeout TO 0') if Gitlab::Database.postgresql? # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
+      execute('SET LOCAL statement_timeout TO 0') # see https://gitlab.com/gitlab-org/gitlab-foss/issues/48967
 
       execute("UPDATE site_statistics SET wikis_count = (SELECT COUNT(*) FROM project_features WHERE wiki_access_level != 0)")
     end

doc/development/sql.md

@@ -108,15 +108,11 @@ class AddUsersLowerUsernameEmailIndexes < ActiveRecord::Migration[4.2]
   disable_ddl_transaction!
 
   def up
-    return unless Gitlab::Database.postgresql?
-
     execute 'CREATE INDEX CONCURRENTLY index_on_users_lower_username ON users (LOWER(username));'
     execute 'CREATE INDEX CONCURRENTLY index_on_users_lower_email ON users (LOWER(email));'
   end
 
   def down
-    return unless Gitlab::Database.postgresql?
-
     remove_index :users, :index_on_users_lower_username
     remove_index :users, :index_on_users_lower_email
   end

doc/development/verifying_database_capabilities.md

@@ -6,22 +6,16 @@ necessary to add database (version) specific behaviour.
 
 To facilitate this we have the following methods that you can use:
 
-- `Gitlab::Database.postgresql?`: returns `true` if PostgreSQL is being used.
-  You can normally just assume this is the case.
 - `Gitlab::Database.version`: returns the PostgreSQL version number as a string
   in the format `X.Y.Z`.
 
 This allows you to write code such as:
 
 ```ruby
-if Gitlab::Database.postgresql?
-  if Gitlab::Database.version.to_f >= 9.6
+if Gitlab::Database.version.to_f >= 9.6
   run_really_fast_query
-  else
-    run_fast_query
-  end
 else
-  run_query
+  run_fast_query
 end
 ```
 

lib/gitlab/background_migration/migrate_legacy_artifacts.rb

@@ -123,8 +123,6 @@ module Gitlab
       end
 
       def add_missing_db_timezone
-        return '' unless Gitlab::Database.postgresql?
-
         'at time zone \'UTC\''
       end
     end