Add soft clear preserving oplog state

Author: simolus3

crates/core/src/view_admin.rs

@@ -150,14 +150,21 @@ fn powersync_clear_impl(
 ) -> Result<String, PowerSyncError> {
     let local_db = ctx.db_handle();
 
-    let clear_local = args[0].int();
+    let flags = PowerSyncClearFlags(args[0].int());
+
+    if !flags.soft_clear() {
+        // With a soft clear, we want to delete public data while keeping internal data around. When
+        // connect() is called with compatible JWTs yielding a large overlap of buckets, this can
+        // speed up the next sync.
+        local_db.exec_safe("DELETE FROM ps_oplog; DELETE FROM ps_buckets")?;
+    } else {
+        local_db.exec_safe("UPDATE ps_buckets SET last_applied_op = 0")?;
+    }
 
     // language=SQLite
     local_db.exec_safe(
         "\
-DELETE FROM ps_oplog;
 DELETE FROM ps_crud;
-DELETE FROM ps_buckets;
 DELETE FROM ps_untyped;
 DELETE FROM ps_updated_rows;
 DELETE FROM ps_kv WHERE key != 'client_id';
@@ -166,7 +173,7 @@ DELETE FROM ps_stream_subscriptions;
 ",
     )?;
 
-    let table_glob = if clear_local != 0 {
+    let table_glob = if flags.clear_local() {
         "ps_data_*"
     } else {
         "ps_data__*"
@@ -199,6 +206,22 @@ DELETE FROM {table};",
     Ok(String::from(""))
 }
 
+#[derive(Clone, Copy)]
+struct PowerSyncClearFlags(i32);
+
+impl PowerSyncClearFlags {
+    const MASK_CLEAR_LOCAL: i32 = 0x01;
+    const MASK_SOFT_CLEAR: i32 = 0x02;
+
+    fn clear_local(self) -> bool {
+        self.0 & Self::MASK_CLEAR_LOCAL != 0
+    }
+
+    fn soft_clear(self) -> bool {
+        self.0 & Self::MASK_SOFT_CLEAR != 0
+    }
+}
+
 create_auto_tx_function!(powersync_clear_tx, powersync_clear_impl);
 create_sqlite_text_fn!(powersync_clear, powersync_clear_tx, "powersync_clear");
 

dart/test/sync_test.dart

@@ -370,6 +370,38 @@ void _syncTests<T>({
     expect(db.select('SELECT * FROM ps_sync_state'), hasLength(0));
   });
 
+  test('can soft clear', () {
+    invokeControl('start', null);
+    pushCheckpoint(buckets: [bucketDescription('a', count: 1)]);
+    pushSyncData('a', '1', 'row-0', 'PUT', {'col': 'hi'});
+    pushCheckpointComplete();
+
+    expect(db.select('SELECT * FROM items'), hasLength(1));
+
+    // Soft clear
+    db.execute('SELECT powersync_clear(2)');
+    db.select('select powersync_replace_schema(?)', [json.encode(testSchema)]);
+    expect(db.select('SELECT * FROM items'), hasLength(0));
+
+    final request = invokeControl('start', null);
+    expect(
+      request,
+      contains(containsPair(
+        'EstablishSyncStream',
+        {
+          // Should request state from before clear
+          'request': containsPair('buckets', [
+            {'name': 'a', 'after': '1'}
+          ]),
+        },
+      )),
+    );
+
+    pushCheckpoint(buckets: [bucketDescription('a', count: 1)]);
+    pushCheckpointComplete();
+    expect(db.select('SELECT * FROM items'), hasLength(1));
+  });
+
   test('persists download progress', () {
     const bucket = 'bkt';
     void expectProgress(int atLast, int sinceLast) {