feat: optimize SQLite PRAGMAs (WAL, mmap 256MB, cache 32MB, temp_store) and add compound indexes

tests/test_api.py

@@ -1042,3 +1042,76 @@ def test_http_connection_pooling():
     assert c3 is not c1
     assert not c3.is_closed
     asyncio.run(close_http_client())
+
+
+def test_sqlite_pragma_tuning_and_composite_indexes():
+    from app.database import get_db, get_db_connection
+
+    # 1. Verify PRAGMAs on a newly opened connection
+    conn = get_db_connection()
+    try:
+        j_mode = conn.execute("PRAGMA journal_mode;").fetchone()[0]
+        sync = conn.execute("PRAGMA synchronous;").fetchone()[0]
+        mmap = conn.execute("PRAGMA mmap_size;").fetchone()[0]
+        cache = conn.execute("PRAGMA cache_size;").fetchone()[0]
+        temp = conn.execute("PRAGMA temp_store;").fetchone()[0]
+        fk = conn.execute("PRAGMA foreign_keys;").fetchone()[0]
+
+        assert j_mode.lower() == "wal"
+        assert sync == 1  # NORMAL
+        assert mmap == 268435456  # 256MB mmap
+        assert cache == -32000  # 32MB cache
+        assert temp == 2  # MEMORY
+        assert fk == 1  # foreign keys ON
+
+        # 2. Verify all composite indexes exist in sqlite_master
+        index_rows = conn.execute(
+            "SELECT name, tbl_name, sql FROM sqlite_master WHERE type = 'index'"
+        ).fetchall()
+        index_names = {r["name"] for r in index_rows}
+
+        expected_indexes = {
+            "idx_vocab_user_created",
+            "idx_vocab_user_srs_state",
+            "idx_vocab_user_srs_created",
+            "idx_vocab_user_term_nocase",
+            "idx_books_user_updated",
+            "idx_srs_card",
+            "idx_srs_reviewed",
+            "idx_sessions_user",
+        }
+        for idx in expected_indexes:
+            assert idx in index_names, f"Expected index {idx} not found in database!"
+
+        # 3. Verify EXPLAIN QUERY PLAN uses the composite indexes
+        plan1 = conn.execute(
+            "EXPLAIN QUERY PLAN SELECT * FROM vocabulary_cards WHERE user_id = ? ORDER BY created_at DESC LIMIT 20",
+            (1,),
+        ).fetchall()
+        plan1_str = " ".join([r[3] for r in plan1])
+        assert "idx_vocab_user_created" in plan1_str
+
+        plan2 = conn.execute(
+            "EXPLAIN QUERY PLAN SELECT * FROM vocabulary_cards WHERE user_id = ? AND srs_state = 'new' ORDER BY created_at DESC LIMIT 10",
+            (1,),
+        ).fetchall()
+        plan2_str = " ".join([r[3] for r in plan2])
+        assert "idx_vocab_user_srs_created" in plan2_str or "idx_vocab_user_created" in plan2_str
+
+        plan3 = conn.execute(
+            "EXPLAIN QUERY PLAN SELECT * FROM books WHERE user_id = ? ORDER BY updated_at DESC",
+            (1,),
+        ).fetchall()
+        plan3_str = " ".join([r[3] for r in plan3])
+        assert "idx_books_user_updated" in plan3_str
+
+        plan4 = conn.execute(
+            "EXPLAIN QUERY PLAN SELECT * FROM srs_logs WHERE card_id = ?",
+            (1,),
+        ).fetchall()
+        plan4_str = " ".join([r[3] for r in plan4])
+        assert "idx_srs_card" in plan4_str
+
+    finally:
+        conn.close()
+