Add indexes to all geo event foreign keys

Because the Geo Event tables do a `on_delete: :cascade`, the foreign
keys in `geo_event_log` need to have an index. Otherwise the deletion
would be very slow.

See
https://docs.gitlab.com/ee/development/migration_style_guide.html#adding-foreign-key-constraints

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/7955

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20181013005024) do
+ActiveRecord::Schema.define(version: 20181017131623) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1123,13 +1123,18 @@ ActiveRecord::Schema.define(version: 20181013005024) do
     t.integer "cache_invalidation_event_id", limit: 8
   end
 
-  add_index "geo_event_log", ["cache_invalidation_event_id"], name: "index_geo_event_log_on_cache_invalidation_event_id", using: :btree
-  add_index "geo_event_log", ["repositories_changed_event_id"], name: "index_geo_event_log_on_repositories_changed_event_id", using: :btree
-  add_index "geo_event_log", ["repository_created_event_id"], name: "index_geo_event_log_on_repository_created_event_id", using: :btree
-  add_index "geo_event_log", ["repository_deleted_event_id"], name: "index_geo_event_log_on_repository_deleted_event_id", using: :btree
-  add_index "geo_event_log", ["repository_renamed_event_id"], name: "index_geo_event_log_on_repository_renamed_event_id", using: :btree
-  add_index "geo_event_log", ["repository_updated_event_id"], name: "index_geo_event_log_on_repository_updated_event_id", using: :btree
-  add_index "geo_event_log", ["reset_checksum_event_id"], name: "index_geo_event_log_on_reset_checksum_event_id", using: :btree
+  add_index "geo_event_log", ["cache_invalidation_event_id"], name: "index_geo_event_log_on_cache_invalidation_event_id", where: "(cache_invalidation_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["hashed_storage_attachments_event_id"], name: "index_geo_event_log_on_hashed_storage_attachments_event_id", where: "(hashed_storage_attachments_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["hashed_storage_migrated_event_id"], name: "index_geo_event_log_on_hashed_storage_migrated_event_id", where: "(hashed_storage_migrated_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["job_artifact_deleted_event_id"], name: "index_geo_event_log_on_job_artifact_deleted_event_id", where: "(job_artifact_deleted_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["lfs_object_deleted_event_id"], name: "index_geo_event_log_on_lfs_object_deleted_event_id", where: "(lfs_object_deleted_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["repositories_changed_event_id"], name: "index_geo_event_log_on_repositories_changed_event_id", where: "(repositories_changed_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["repository_created_event_id"], name: "index_geo_event_log_on_repository_created_event_id", where: "(repository_created_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["repository_deleted_event_id"], name: "index_geo_event_log_on_repository_deleted_event_id", where: "(repository_deleted_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["repository_renamed_event_id"], name: "index_geo_event_log_on_repository_renamed_event_id", where: "(repository_renamed_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["repository_updated_event_id"], name: "index_geo_event_log_on_repository_updated_event_id", where: "(repository_updated_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["reset_checksum_event_id"], name: "index_geo_event_log_on_reset_checksum_event_id", where: "(reset_checksum_event_id IS NOT NULL)", using: :btree
+  add_index "geo_event_log", ["upload_deleted_event_id"], name: "index_geo_event_log_on_upload_deleted_event_id", where: "(upload_deleted_event_id IS NOT NULL)", using: :btree
 
   create_table "geo_hashed_storage_attachments_events", id: :bigserial, force: :cascade do |t|
     t.integer "project_id", null: false

ee/changelogs/unreleased/tc-add-missing-geo-event-indexes.yml

+---
+title: Add indexes to all geo event foreign keys
+merge_request: 7990
+author:
+type: performance

ee/db/migrate/20181017131623_add_missing_geo_even_log_indexes.rb

+# frozen_string_literal: true
+
+class AddMissingGeoEvenLogIndexes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEXED_COLUMNS = %i[cache_invalidation_event_id
+                       repositories_changed_event_id
+                       repository_created_event_id
+                       repository_deleted_event_id
+                       repository_renamed_event_id
+                       repository_updated_event_id
+                       reset_checksum_event_id]
+
+  OTHER_COLUMNS = %i[hashed_storage_migrated_event_id
+                     lfs_object_deleted_event_id
+                     hashed_storage_attachments_event_id
+                     job_artifact_deleted_event_id
+                     upload_deleted_event_id]
+
+  disable_ddl_transaction!
+
+  def up
+    # Remove existing indexes that aren't partial
+    INDEXED_COLUMNS.each do |col|
+      remove_concurrent_index(:geo_event_log, col)
+    end
+
+    # Create partial indexes on all
+    (INDEXED_COLUMNS + OTHER_COLUMNS).each do |col|
+      add_concurrent_index(:geo_event_log,
+                           col,
+                           where: "#{col} IS NOT NULL")
+    end
+  end
+
+  def down
+    # Rollback all partial indexes
+    (INDEXED_COLUMNS + OTHER_COLUMNS).each do |col|
+      remove_concurrent_index(:geo_event_log, col)
+    end
+
+    # Recreate full indexes
+    INDEXED_COLUMNS.each do |col|
+      add_concurrent_index(:geo_event_log, col)
+    end
+  end
+end