Implement write checkpoint workaround for Aurora Postgres.

Author: rkistner

packages/service-core/src/util/utils.ts

@@ -119,9 +119,13 @@ export async function createWriteCheckpoint(
   bucketStorage: storage.BucketStorageFactory,
   user_id: string
 ): Promise<bigint> {
-  const [{ lsn }] = pgwireRows(
-    await retriedQuery(db, `SELECT pg_logical_emit_message(false, 'powersync', 'ping') as lsn`)
-  );
+  // On most Postgres versions, pg_logical_emit_message() returns the correct LSN.
+  // However, on Aurora (Postgres compatible), it can return an entirely different LSN,
+  // causing the write checkpoints to never be replicated back to the client.
+  // For those, we need to use pg_current_wal_lsn() instead.
+  const [{ lsn }] = pgwireRows(await retriedQuery(db, `SELECT pg_current_wal_lsn() as lsn`));
+
+  await retriedQuery(db, `SELECT pg_logical_emit_message(false, 'powersync', 'ping')`);
 
   const id = await bucketStorage.createWriteCheckpoint(user_id, { '1': lsn });
   logger.info(`Write checkpoint 2: ${JSON.stringify({ lsn, id: String(id) })}`);