From 29c6455de4aa6ec54ce2e251d23d3d517d13074a Mon Sep 17 00:00:00 2001
From: Christiaan Landman <chriz.ek@gmail.com>
Date: Thu, 31 Jul 2025 11:43:33 +0200
Subject: [PATCH] Only calling db.export() if a persister is specified,
 exporting the db is not needed if writing would be a no-op. Improves
 performance.

---
 .changeset/short-hotels-grow.md             |  5 +++++
 packages/adapter-sql-js/src/SQLJSAdapter.ts | 19 ++++++++++---------
 2 files changed, 15 insertions(+), 9 deletions(-)
 create mode 100644 .changeset/short-hotels-grow.md

diff --git a/.changeset/short-hotels-grow.md b/.changeset/short-hotels-grow.md
new file mode 100644
index 000000000..3a6d422a2
--- /dev/null
+++ b/.changeset/short-hotels-grow.md
@@ -0,0 +1,5 @@
+---
+'@powersync/adapter-sql-js': patch
+---
+
+Only calling `db.export()` if a persister is specified, otherwise it is no-op. Improves in-memory performance.
diff --git a/packages/adapter-sql-js/src/SQLJSAdapter.ts b/packages/adapter-sql-js/src/SQLJSAdapter.ts
index edc3aa602..4d35ee9f7 100644
--- a/packages/adapter-sql-js/src/SQLJSAdapter.ts
+++ b/packages/adapter-sql-js/src/SQLJSAdapter.ts
@@ -29,7 +29,7 @@ export interface SQLJSOpenOptions extends SQLOpenOptions {
 }
 
 export interface ResolvedSQLJSOpenOptions extends SQLJSOpenOptions {
-  persister: SQLJSPersister;
+  persister?: SQLJSPersister;
   logger: ILogger;
 }
 
@@ -96,21 +96,19 @@ export class SQLJSDBAdapter extends BaseObserver<DBAdapterListener> implements D
     });
 
     this.writeScheduler = new ControlledExecutor(async (db: SQLJs.Database) => {
+      if (!this.options.persister) {
+        return;
+      }
+
       await this.options.persister.writeFile(db.export());
     });
   }
 
   protected resolveOptions(options: SQLJSOpenOptions): ResolvedSQLJSOpenOptions {
-    const persister = options.persister ?? {
-      readFile: async () => null,
-      writeFile: async () => {}
-    };
-
     const logger = options.logger ?? createLogger('SQLJSDBAdapter');
 
     return {
       ...options,
-      persister,
       logger
     };
   }
@@ -125,7 +123,7 @@ export class SQLJSDBAdapter extends BaseObserver<DBAdapterListener> implements D
         this.options.logger.error('[stderr]', text);
       }
     });
-    const existing = await this.options.persister.readFile();
+    const existing = await this.options.persister?.readFile();
     const db = new SQL.Database(existing);
     this.dbP = db['db'];
     this._db = db;
@@ -262,7 +260,10 @@ export class SQLJSDBAdapter extends BaseObserver<DBAdapterListener> implements D
       const db = await this.getDB();
       const result = await fn(this.generateLockContext());
 
-      this.writeScheduler.schedule(db);
+      // No point to schedule a write if there's no persister.
+      if (this.options.persister) {
+        this.writeScheduler.schedule(db);
+      }
 
       const notification: BatchedUpdateNotification = {
         rawUpdates: [],