PERF: Add index to speed up ReindexSearch job (#20151)

app/models/post.rb

@@ -1290,6 +1290,7 @@ end
 #  idx_posts_user_id_deleted_at                           (user_id) WHERE (deleted_at IS NULL)
 #  index_for_rebake_old                                   (id) WHERE (((baked_version IS NULL) OR (baked_version < 2)) AND (deleted_at IS NULL))
 #  index_posts_on_id_and_baked_version                    (id DESC,baked_version) WHERE (deleted_at IS NULL)
+#  index_posts_on_id_topic_id_where_not_deleted_or_empty  (id,topic_id) WHERE ((deleted_at IS NULL) AND (raw <> ''::text))
 #  index_posts_on_image_upload_id                         (image_upload_id)
 #  index_posts_on_reply_to_post_number                    (reply_to_post_number)
 #  index_posts_on_topic_id_and_percent_rank               (topic_id,percent_rank)

db/migrate/20230202204937_add_index_to_posts_where_not_deleted_or_empty.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class AddIndexToPostsWhereNotDeletedOrEmpty < ActiveRecord::Migration[7.0]
+  disable_ddl_transaction!
+
+  def up
+    execute <<~SQL
+      DROP INDEX CONCURRENTLY IF EXISTS index_posts_on_id_topic_id_where_not_deleted_or_empty
+    SQL
+
+    execute <<~SQL
+      CREATE INDEX CONCURRENTLY index_posts_on_id_topic_id_where_not_deleted_or_empty ON posts (id, topic_id) where deleted_at IS NULL AND raw <> ''
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      DROP INDEX IF EXISTS index_posts_on_id_topic_id_where_not_deleted_or_empty
+    SQL
+  end
+end