Fix SQLite concurrency issues with WAL mode and timeouts

backend/app/database/connection.py

@@ -7,26 +7,37 @@
 @contextmanager
 def get_db_connection() -> Generator[sqlite3.Connection, None, None]:
     """
-    SQLite connection context manager with all integrity constraints enforced.
+    SQLite connection context manager with concurrency optimization and integrity constraints.
 
-    - Enables all major relational integrity PRAGMAs
+    - Enables WAL mode for better concurrent access
+    - Configures timeouts and concurrency PRAGMAs
+    - Enforces all major relational integrity PRAGMAs
     - Works for both single and multi-step transactions
     - Automatically commits on success or rolls back on failure
     """
-    conn = sqlite3.connect(DATABASE_PATH)
-
-    # --- Strict enforcement of all relational and logical rules ---
-    conn.execute("PRAGMA foreign_keys = ON;")  # Enforce FK constraints
-    conn.execute("PRAGMA ignore_check_constraints = OFF;")  # Enforce CHECK constraints
-    conn.execute("PRAGMA recursive_triggers = ON;")  # Allow nested triggers
-    conn.execute("PRAGMA defer_foreign_keys = OFF;")  # Immediate FK checking
-    conn.execute("PRAGMA case_sensitive_like = ON;")  # Make LIKE case-sensitive
-
+    conn = None
     try:
+        conn = sqlite3.connect(DATABASE_PATH, timeout=30.0)
+
+        # --- Concurrency and performance optimizations ---
+        conn.execute("PRAGMA journal_mode = WAL;")  # Enable WAL mode for better concurrency
+        conn.execute("PRAGMA synchronous = NORMAL;")  # Balance safety and performance
+        conn.execute("PRAGMA cache_size = -64000;")  # 64MB cache
+        conn.execute("PRAGMA temp_store = MEMORY;")  # Store temp tables in memory
+        conn.execute("PRAGMA mmap_size = 268435456;")  # 256MB memory-mapped I/O
+        conn.execute("PRAGMA busy_timeout = 30000;")  # 30 second timeout for locks
+
+        # --- Strict enforcement of all relational and logical rules ---
+        conn.execute("PRAGMA foreign_keys = ON;")  # Enforce FK constraints
+        conn.execute("PRAGMA ignore_check_constraints = OFF;")  # Enforce CHECK constraints
+        conn.execute("PRAGMA defer_foreign_keys = OFF;")  # Immediate FK checking
+
         yield conn
         conn.commit()
     except Exception:
-        conn.rollback()
+        if conn:
+            conn.rollback()
         raise
     finally:
-        conn.close()
+        if conn:
+            conn.close()