sqlite - feat: Add warning for WAL mode with in-memory SQLite databases (#1832)

* sqlite - feat: Add warning logging for WAL mode on in-memory databases

When WAL mode is requested for an in-memory database (:memory: or empty
string), the code now logs a warning message to inform developers that
the option will be ignored, rather than silently passing the PRAGMA
to SQLite which would silently ignore it.

https://claude.ai/code/session_01ESQBgre2YMC66TdTca7YdG

* Update test.ts

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: jaredwray

packages/sqlite/README.md

@@ -48,7 +48,7 @@ const keyv = new Keyv({ store: keyvSqlite });
 - `table` - The table name to use for storage (default: `'keyv'`)
 - `busyTimeout` - Sets a busy handler that sleeps for a specified amount of time when a table is locked
 - `wal` - Enable [Write-Ahead Logging](https://sqlite.org/wal.html) mode for better concurrency and performance (default: `false`)
-  - **Note:** WAL mode is not supported for in-memory databases (`:memory:`). SQLite will silently ignore the WAL mode request and remain in "memory" journal mode.
+  - **Note:** WAL mode is not supported for in-memory databases (`:memory:`). A warning will be logged and the option will be ignored.
 - `keySize` - The maximum key size in bytes (default: `255`, max: `65535`)
 
 You can also use a helper function to create `Keyv` with `KeyvSqlite` store.

packages/sqlite/src/index.ts

@@ -58,9 +58,14 @@ export class KeyvSqlite extends EventEmitter implements KeyvStoreAdapter {
 				const close = promisify(database.close).bind(database);
 
 				if (options.wal) {
-					// WAL mode doesn't work with in-memory databases, but SQLite silently
-					// ignores the request and keeps "memory" mode, so we do the same
-					await query("PRAGMA journal_mode=WAL");
+					const isInMemory = options.db === ":memory:" || options.db === "";
+					if (isInMemory) {
+						console.warn(
+							"@keyv/sqlite: WAL mode is not supported for in-memory databases. The wal option will be ignored.",
+						);
+					} else {
+						await query("PRAGMA journal_mode=WAL");
+					}
 				}
 
 				return {

packages/sqlite/test/test.ts

@@ -313,3 +313,22 @@ test.it(
 		await keyv.disconnect();
 	},
 );
+
+test.it("WAL mode with in-memory database logs a warning", async (t) => {
+	const warnSpy = test.vi.spyOn(console, "warn").mockImplementation(() => {});
+
+	const keyv = new KeyvSqlite({
+		uri: "sqlite://:memory:",
+		wal: true,
+	});
+
+	// Wait for the database to initialize (the warn happens during initialization)
+	await keyv.query("SELECT 1");
+
+	t.expect(warnSpy).toHaveBeenCalledWith(
+		"@keyv/sqlite: WAL mode is not supported for in-memory databases. The wal option will be ignored.",
+	);
+
+	warnSpy.mockRestore();
+	await keyv.disconnect();
+});