Cache prepared statements per database connection

src/lib/server/db/index.ts

@@ -391,6 +391,21 @@ export function db(): Database.Database {
         throw err;
     }
 
+    // Cache only runtime queries, after migrations have finished. Statements
+    // belong to this connection, so reopening the DB starts with an empty cache.
+    // Callers share statement options (e.g. raw()); use consistent options for
+    // identical SQL and pass values to run/get/all rather than binding permanently.
+    const statements = new Map<string, Database.Statement>();
+    const prepare = handle.prepare.bind(handle);
+    handle.prepare = ((sql: string) => {
+        let statement = statements.get(sql);
+        if (!statement) {
+            statement = prepare(sql);
+            statements.set(sql, statement);
+        }
+        return statement;
+    }) as typeof handle.prepare;
+
     _db = handle;
     return _db;
 }