Add partial index on projects for index-only scans.
This helps with queries that get project ids based on the - comparably rare - visibility levels 10 and 20. For these, postgres can now leverage the partial index for a index-only scan to improve performance. Example queries: SELECT id FROM projects WHERE visibility_level IN (10,20) SELECT id FROM projects WHERE visibility_level IN (10) For MySQL, this results in a full index on id because MySQL omits the WHERE clause. That is, the index is a duplicate of the primary key basically.
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class AddPartialIndexToProjectsForIndexOnlyScans < ActiveRecord::Migration
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include Gitlab::Database::MigrationHelpers
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DOWNTIME = false
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INDEX_NAME = 'index_projects_on_id_partial_for_visibility'
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disable_ddl_transaction!
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# Adds a partial index to leverage index-only scans when looking up project ids
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def up
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unless index_exists?(:projects, :id, name: INDEX_NAME)
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add_concurrent_index :projects, :id, name: INDEX_NAME, unique: true, where: 'visibility_level IN (10,20)'
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end
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end
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def down
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if index_exists?(:projects, :id, name: INDEX_NAME)
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remove_concurrent_index :projects, :id, name: INDEX_NAME, unique: true, where: 'visibility_level IN (10,20)'
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end
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end
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end
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@ -11,7 +11,7 @@
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#
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# It's strongly recommended that you check this file into your version control system.
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ActiveRecord::Schema.define(version: 20180208183958) do
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ActiveRecord::Schema.define(version: 20180213131630) do
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# These are extensions that must be enabled in order to support this database
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enable_extension "plpgsql"
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@ -1468,6 +1468,7 @@ ActiveRecord::Schema.define(version: 20180208183958) do
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add_index "projects", ["created_at"], name: "index_projects_on_created_at", using: :btree
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add_index "projects", ["creator_id"], name: "index_projects_on_creator_id", using: :btree
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add_index "projects", ["description"], name: "index_projects_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
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add_index "projects", ["id"], name: "index_projects_on_id_partial_for_visibility", unique: true, where: "(visibility_level = ANY (ARRAY[10, 20]))", using: :btree
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add_index "projects", ["last_activity_at"], name: "index_projects_on_last_activity_at", using: :btree
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add_index "projects", ["last_repository_check_failed"], name: "index_projects_on_last_repository_check_failed", using: :btree
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add_index "projects", ["last_repository_updated_at"], name: "index_projects_on_last_repository_updated_at", using: :btree
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