Optimize all_resource_timestamps() (#3597)

Author: leplatrem

kinto/core/storage/postgresql/__init__.py

@@ -79,7 +79,7 @@ class Storage(StorageBase, MigratorMixin):
 
     # MigratorMixin attributes.
     name = "storage"
-    schema_version = 24
+    schema_version = 25
     schema_file = os.path.join(HERE, "schema.sql")
     migrations_directory = os.path.join(HERE, "migrations")
 
@@ -252,20 +252,20 @@ def all_resources_timestamps(self, resource_name):
         WITH existing_timestamps AS (
           -- Timestamp of latest object by parent_id.
           (
-            SELECT parent_id, MAX(last_modified) AS last_modified
+            SELECT DISTINCT ON (parent_id) parent_id, last_modified
             FROM objects
             WHERE resource_name = :resource_name
-            GROUP BY parent_id
+            ORDER BY parent_id, last_modified DESC
           )
           -- Timestamp of resources without sub-objects.
-          UNION
+          UNION ALL
           (
             SELECT parent_id, last_modified
             FROM timestamps
             WHERE resource_name = :resource_name
           )
         )
-        SELECT parent_id, MAX(as_epoch(last_modified)) AS last_modified
+        SELECT parent_id, as_epoch(MAX(last_modified)) AS last_modified
           FROM existing_timestamps
           GROUP BY parent_id
           ORDER BY last_modified DESC

kinto/core/storage/postgresql/migrations/migration_024_025.sql

@@ -0,0 +1,6 @@
+CREATE INDEX IF NOT EXISTS idx_objects_parent_id_record_last_modified
+    ON objects (parent_id, last_modified DESC)
+    WHERE resource_name = 'record';
+
+-- Bump storage schema version.
+INSERT INTO metadata (name, value) VALUES ('storage_schema_version', '25');

kinto/core/storage/postgresql/schema.sql

@@ -49,10 +49,14 @@ CREATE INDEX IF NOT EXISTS idx_objects_last_modified_epoch
     ON objects(as_epoch(last_modified));
 CREATE INDEX IF NOT EXISTS idx_objects_resource_name_parent_id_deleted
     ON objects(resource_name, parent_id, deleted);
+-- Index for collections timestamps
+CREATE INDEX IF NOT EXISTS idx_objects_parent_id_record_last_modified
+    ON objects (parent_id, last_modified DESC)
+    WHERE resource_name = 'record';
 -- Index for history plugin trimming.
 CREATE INDEX IF NOT EXISTS idx_objects_history_userid_and_resourcename
-  ON objects ((data->'user_id'), (data->'resource_name'))
-  WHERE resource_name = 'history';
+    ON objects ((data->'user_id'), (data->'resource_name'))
+    WHERE resource_name = 'history';
 
 CREATE TABLE IF NOT EXISTS timestamps (
   parent_id TEXT NOT NULL COLLATE "C",
@@ -136,4 +140,4 @@ INSERT INTO metadata (name, value) VALUES ('created_at', NOW()::TEXT);
 
 -- Set storage schema version.
 -- Should match ``kinto.core.storage.postgresql.PostgreSQL.schema_version``
-INSERT INTO metadata (name, value) VALUES ('storage_schema_version', '24');
+INSERT INTO metadata (name, value) VALUES ('storage_schema_version', '25');