From 609a434c6dc2c6d4aafb359348c129fc01d264e3 Mon Sep 17 00:00:00 2001
From: Stan Hu <stanhu@gmail.com>
Date: Tue, 6 Mar 2018 13:30:10 -0800
Subject: [PATCH] Adding missing indexes on taggings table

API requests were timing out because `tag_id` was missing an index. These
migrations were imported by running https://github.com/mbleigh/acts-as-taggable-on#post-installation:

```
bundle exec rake acts_as_taggable_on_engine:install:migrations
```

It looks like the `acts-as-tagglable` gem added the indexes in v4.0.0, but
when we upgraded from v3.5.0 (back in 2016 via
f571aeb5ce38dce1a9e5f58d76360836d4a8f8a0) we did not add them.

On staging, there are about 10.7 million rows on the `taggings` table. It took about 30 seconds for each index to be created.

On production, there are about 17.4 million rows, so I suspect the time to be about a minute per index.

Closes #43927
---
 ...h-add-missing-acts-as-taggable-indices.yml |  5 +++++
 ...sing_indexes_acts_as_taggable_on_engine.rb | 21 +++++++++++++++++++
 db/schema.rb                                  |  2 ++
 3 files changed, 28 insertions(+)
 create mode 100644 changelogs/unreleased/sh-add-missing-acts-as-taggable-indices.yml
 create mode 100644 db/migrate/20180306134842_add_missing_indexes_acts_as_taggable_on_engine.rb

diff --git a/changelogs/unreleased/sh-add-missing-acts-as-taggable-indices.yml b/changelogs/unreleased/sh-add-missing-acts-as-taggable-indices.yml
new file mode 100644
index 00000000000..d9a1a0db9e8
--- /dev/null
+++ b/changelogs/unreleased/sh-add-missing-acts-as-taggable-indices.yml
@@ -0,0 +1,5 @@
+---
+title: Adding missing indexes on taggings table
+merge_request:
+author:
+type: performance
diff --git a/db/migrate/20180306134842_add_missing_indexes_acts_as_taggable_on_engine.rb b/db/migrate/20180306134842_add_missing_indexes_acts_as_taggable_on_engine.rb
new file mode 100644
index 00000000000..06e402adcd7
--- /dev/null
+++ b/db/migrate/20180306134842_add_missing_indexes_acts_as_taggable_on_engine.rb
@@ -0,0 +1,21 @@
+# This migration comes from acts_as_taggable_on_engine (originally 6)
+#
+# It has been modified to handle no-downtime GitLab migrations. Several
+# indexes have been removed since they are not needed for GitLab.
+class AddMissingIndexesActsAsTaggableOnEngine < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :taggings, :tag_id unless index_exists? :taggings, :tag_id
+    add_concurrent_index :taggings, [:taggable_id, :taggable_type] unless index_exists? :taggings, [:taggable_id, :taggable_type]
+  end
+
+  def down
+    remove_concurrent_index :taggings, :tag_id
+    remove_concurrent_index :taggings, [:taggable_id, :taggable_type]
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index b93e6fa594b..9fabde75625 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -1733,7 +1733,9 @@ ActiveRecord::Schema.define(version: 20180307012445) do
   end
 
   add_index "taggings", ["tag_id", "taggable_id", "taggable_type", "context", "tagger_id", "tagger_type"], name: "taggings_idx", unique: true, using: :btree
+  add_index "taggings", ["tag_id"], name: "index_taggings_on_tag_id", using: :btree
   add_index "taggings", ["taggable_id", "taggable_type", "context"], name: "index_taggings_on_taggable_id_and_taggable_type_and_context", using: :btree
+  add_index "taggings", ["taggable_id", "taggable_type"], name: "index_taggings_on_taggable_id_and_taggable_type", using: :btree
 
   create_table "tags", force: :cascade do |t|
     t.string "name"