Improved performance fetching posts (#20460)

ref https://linear.app/tryghost/issue/ONC-111
- added composite index to posts_tags for post_id,tag_id for faster
lookup
- added composite index to posts for updated_at; this is commonly used
by get helpers on the front end to display data like the latest posts

In testing, this provided a very dramatic improvement for simple get
helper requests like 'filter="id:-{{post.id}}+tag:sampleTag" limit="3"'
which are by default sorted by updated_at desc. I'm not entirely clear
why when sorting by published_at we do not need a composite index - so
far it doesn't seem to be necessary. This should cover the primary cases
for get helpers - the latest posts with a given tag or set of tags.

ghost/core/core/server/data/migrations/versions/5.87/2024-06-25-12-08-20-add-posts-tags-post-tag-index.js

@@ -0,0 +1,26 @@
+const logging = require('@tryghost/logging');
+const {createNonTransactionalMigration} = require('../../utils');
+const {addIndex, dropIndex} = require('../../../schema/commands');
+
+module.exports = createNonTransactionalMigration(
+    async function up(knex) {
+        await addIndex('posts_tags', ['post_id', 'tag_id'], knex);
+    },
+    async function down(knex) {
+        try {
+            await dropIndex('posts_tags', ['post_id', 'tag_id'], knex);
+        } catch (err) {
+            if (err.code === 'ER_DROP_INDEX_FK') {
+                logging.error({
+                    message: 'Error dropping index over posts_tags(post_id, tag_id), re-adding index for post_id'
+                });
+
+                await addIndex('posts_tags', ['post_id'], knex);
+                await dropIndex('posts_tags', ['post_id', 'tag_id'], knex);
+                return;
+            }
+
+            throw err;
+        }
+    }
+);

ghost/core/core/server/data/migrations/versions/5.87/2024-06-25-12-08-45-add-posts-type-status-updated-at-index.js

@@ -1,4 +1,4 @@
 // For information on writing migrations, see https://www.notion.so/ghost/Database-migrations-eb5b78c435d741d2b34a582d57c24253
 const {createAddIndexMigration} = require('../../utils');
 
-module.exports = createAddIndexMigration('posts',['type','status']);
+module.exports = createAddIndexMigration('posts',['type','status','updated_at']);

ghost/core/core/server/data/schema/schema.js

@@ -94,7 +94,7 @@ module.exports = {
         newsletter_id: {type: 'string', maxlength: 24, nullable: true, references: 'newsletters.id'},
         show_title_and_feature_image: {type: 'boolean', nullable: false, defaultTo: true},
         '@@INDEXES@@': [
-            ['type','status']
+            ['type','status','updated_at']
         ],
         '@@UNIQUE_CONSTRAINTS@@': [
             ['slug', 'type']
@@ -298,7 +298,10 @@ module.exports = {
         id: {type: 'string', maxlength: 24, nullable: false, primary: true},
         post_id: {type: 'string', maxlength: 24, nullable: false, references: 'posts.id'},
         tag_id: {type: 'string', maxlength: 24, nullable: false, references: 'tags.id'},
-        sort_order: {type: 'integer', nullable: false, unsigned: true, defaultTo: 0}
+        sort_order: {type: 'integer', nullable: false, unsigned: true, defaultTo: 0},
+        '@@INDEXES@@': [
+            ['post_id','tag_id']
+        ]
     },
     invites: {
         id: {type: 'string', maxlength: 24, nullable: false, primary: true},

ghost/core/test/unit/server/data/schema/integrity.test.js

@@ -35,7 +35,7 @@ const validateRouteSettings = require('../../../../../core/server/services/route
  */
 describe('DB version integrity', function () {
     // Only these variables should need updating
-    const currentSchemaHash = '45c8072332176e0fe5a4fdff58fb2113';
+    const currentSchemaHash = 'ce97eff9bf1b3c215fed1271f9275f83';
     const currentFixturesHash = 'a489d615989eab1023d4b8af0ecee7fd';
     const currentSettingsHash = '5c957ceb48c4878767d7d3db484c592d';
     const currentRoutesHash = '3d180d52c663d173a6be791ef411ed01';