core: create indices on chat_items for faster pagination (#927)

src/Simplex/Chat/Migrations/M20220811_chat_items_indices.hs

@@ -0,0 +1,13 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module Simplex.Chat.Migrations.M20220811_chat_items_indices where
+
+import Database.SQLite.Simple (Query)
+import Database.SQLite.Simple.QQ (sql)
+
+m20220811_chat_items_indices :: Query
+m20220811_chat_items_indices =
+  [sql|
+CREATE INDEX idx_chat_items_groups ON chat_items(user_id, group_id, item_ts, chat_item_id);
+CREATE INDEX idx_chat_items_contacts ON chat_items(user_id, contact_id, chat_item_id);
+|]

src/Simplex/Chat/Migrations/chat_schema.sql

@@ -382,3 +382,14 @@ CREATE TABLE calls(
   created_at TEXT NOT NULL DEFAULT(datetime('now')),
   updated_at TEXT NOT NULL DEFAULT(datetime('now'))
 );
+CREATE INDEX idx_chat_items_groups ON chat_items(
+  user_id,
+  group_id,
+  item_ts,
+  chat_item_id
+);
+CREATE INDEX idx_chat_items_contacts ON chat_items(
+  user_id,
+  contact_id,
+  chat_item_id
+);