Temporary drop foreign key when database is MySQL

db/schema.rb

@@ -3225,6 +3225,7 @@ ActiveRecord::Schema.define(version: 20181017131623) do
   add_foreign_key "gcp_clusters", "services", on_delete: :nullify
   add_foreign_key "gcp_clusters", "users", on_delete: :nullify
   add_foreign_key "geo_event_log", "geo_cache_invalidation_events", column: "cache_invalidation_event_id", name: "fk_42c3b54bed", on_delete: :cascade
+  add_foreign_key "geo_event_log", "geo_hashed_storage_attachments_events", column: "hashed_storage_attachments_event_id", name: "fk_304067fc30", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_hashed_storage_migrated_events", column: "hashed_storage_migrated_event_id", name: "fk_27548c6db3", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_job_artifact_deleted_events", column: "job_artifact_deleted_event_id", name: "fk_176d3fbb5d", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_lfs_object_deleted_events", column: "lfs_object_deleted_event_id", name: "fk_d5af95fcd9", on_delete: :cascade
@@ -3232,7 +3233,7 @@ ActiveRecord::Schema.define(version: 20181017131623) do
   add_foreign_key "geo_event_log", "geo_repository_created_events", column: "repository_created_event_id", name: "fk_9b9afb1916", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_repository_deleted_events", column: "repository_deleted_event_id", name: "fk_c4b1c1f66e", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_repository_renamed_events", column: "repository_renamed_event_id", name: "fk_86c84214ec", on_delete: :cascade
-  add_foreign_key "geo_event_log", "geo_repository_updated_events", column: "repository_updated_event_id", on_delete: :cascade
+  add_foreign_key "geo_event_log", "geo_repository_updated_events", column: "repository_updated_event_id", name: "fk_78a6492f68", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_reset_checksum_events", column: "reset_checksum_event_id", name: "fk_cff7185ad2", on_delete: :cascade
   add_foreign_key "geo_event_log", "geo_upload_deleted_events", column: "upload_deleted_event_id", name: "fk_c1f241c70d", on_delete: :cascade
   add_foreign_key "geo_hashed_storage_attachments_events", "projects", on_delete: :cascade

ee/db/migrate/20181017131623_add_missing_geo_even_log_indexes.rb

@@ -12,37 +12,83 @@ class AddMissingGeoEvenLogIndexes < ActiveRecord::Migration
                        repository_updated_event_id
                        reset_checksum_event_id]
 
-  OTHER_COLUMNS = %i[hashed_storage_migrated_event_id
+  NON_INDEXED_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]
 
+  MISSING_FK_COLUMNS = %i[hashed_storage_attachments_event_id]
+
   disable_ddl_transaction!
 
   def up
-    # Remove existing indexes that aren't partial
+    # Replace existing indexes with partial indexes
     INDEXED_COLUMNS.each do |col|
+      without_foreign_key(:geo_event_log, col) do
         remove_concurrent_index(:geo_event_log, col)
+        add_concurrent_index_not_null(:geo_event_log, col)
+      end
     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")
+    # Create partial indexes on non-indexed columns
+    NON_INDEXED_COLUMNS.each do |col|
+      add_concurrent_index_not_null(:geo_event_log, col)
+    end
+
+    # Add missing foreign keys
+    MISSING_FK_COLUMNS.each do |col|
+      add_concurrent_foreign_key(:geo_event_log,
+                                 foreign_table_name(col),
+                                 column: col,
+                                 on_delete: :cascade)
     end
   end
 
   def down
-    # Rollback all partial indexes
-    (INDEXED_COLUMNS + OTHER_COLUMNS).each do |col|
+    # Remove missing foreign keys again
+    MISSING_FK_COLUMNS.each do |col|
+      remove_foreign_key(:geo_event_log, column: col)
+    end
+
+    # Drop indexes that didn't exist before
+    NON_INDEXED_COLUMNS.each do |col|
+      without_foreign_key(:geo_event_log, col) do
         remove_concurrent_index(:geo_event_log, col)
       end
+    end
 
     # Recreate full indexes
     INDEXED_COLUMNS.each do |col|
+      without_foreign_key(:geo_event_log, col) do
+        remove_concurrent_index(:geo_event_log, col)
         add_concurrent_index(:geo_event_log, col)
       end
     end
+  end
+
+  private
+
+  def add_concurrent_index_not_null(table, col)
+    add_concurrent_index(table, col, where: "#{col} IS NOT NULL")
+  end
+
+  def without_foreign_key(table, col)
+    return yield unless drop_foreign_key?(table, col)
+
+    begin
+      remove_foreign_key(table, column: col)
+      yield
+    ensure
+      add_concurrent_foreign_key(table, foreign_table_name(col), column: col, on_delete: :cascade)
+    end
+  end
+
+  def drop_foreign_key?(table, col)
+    Gitlab::Database.mysql? && foreign_key_exists?(table, column: col)
+  end
+
+  def foreign_table_name(col)
+    ('geo_' + col.to_s.sub(/_id$/, '')).pluralize
+  end
 end