ai tags: replace tag_id index with (tag_id, score) index.

Index on (tag_id, score) instead of (tag_id) to allow tags to be
filtered and sorted by confidence more efficiently. This index takes up
about the same amount of space as an index on tag_id alone, so including
the score in the index is essentially free.

db/migrate/20220627211714_add_tag_id_and_score_index_to_ai_tags.rb

@@ -0,0 +1,6 @@
+class AddTagIdAndScoreIndexToAITags < ActiveRecord::Migration[7.0]
+  def change
+    add_index :ai_tags, [:tag_id, :score], if_not_exists: true
+    remove_index :ai_tags, :tag_id
+  end
+end

db/structure.sql

@@ -3149,10 +3149,10 @@ CREATE INDEX index_ai_tags_on_score ON public.ai_tags USING btree (score);
 
 
 --
--- Name: index_ai_tags_on_tag_id; Type: INDEX; Schema: public; Owner: -
+-- Name: index_ai_tags_on_tag_id_and_score; Type: INDEX; Schema: public; Owner: -
 --
 
-CREATE INDEX index_ai_tags_on_tag_id ON public.ai_tags USING btree (tag_id);
+CREATE INDEX index_ai_tags_on_tag_id_and_score ON public.ai_tags USING btree (tag_id, score);
 
 
 --
@@ -5975,6 +5975,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20220504235329'),
 ('20220514175125'),
 ('20220525214746'),
-('20220623052547');
+('20220623052547'),
+('20220627211714');