make GSI less shit

dynamodb/update_item.odin

@@ -8,6 +8,7 @@ import "../rocksdb"
 
 // UpdateItem — fetch existing item, apply update plan, write back
 // Uses EXCLUSIVE lock (write operation)
+// ATOMICITY: Uses WriteBatch to ensure base item + all GSI updates are atomic
 //
 // Returns:
 //   - old_item:  the item BEFORE mutations (if it existed), for ReturnValues
@@ -59,7 +60,7 @@ update_item :: proc(
 			return nil, nil, .Serialization_Error
 		}
 		existing_item = decoded
-		// Save old item for ReturnValues
+		// Save old item for ReturnValues (and for GSI cleanup)
 		old_item = item_deep_copy(existing_item)
 	} else if get_err == .NotFound || existing_encoded == nil {
 		// Item doesn't exist yet — start with just the key attributes
@@ -109,9 +110,46 @@ update_item :: proc(
 	}
 	defer delete(encoded_item)
 
-	// Write back to RocksDB
-	put_err := rocksdb.db_put(&engine.db, storage_key, encoded_item)
-	if put_err != .None {
+	// --- ATOMIC WRITE BATCH: base item + all GSI updates ---
+	batch, batch_err := rocksdb.batch_create()
+	if batch_err != .None {
+		item_destroy(&existing_item)
+		if old, has := old_item.?; has {
+			old_copy := old
+			item_destroy(&old_copy)
+		}
+		return nil, nil, .RocksDB_Error
+	}
+	defer rocksdb.batch_destroy(&batch)
+
+	// Add base item write to batch
+	rocksdb.batch_put(&batch, storage_key, encoded_item)
+
+	// Add old GSI entry deletions to batch (if item existed before)
+	if old, has := old_item.?; has {
+		gsi_del_err := gsi_batch_delete_entries(&batch, table_name, old, &metadata)
+		if gsi_del_err != .None {
+			item_destroy(&existing_item)
+			old_copy := old
+			item_destroy(&old_copy)
+			return nil, nil, gsi_del_err
+		}
+	}
+
+	// Add new GSI entry writes to batch
+	gsi_write_err := gsi_batch_write_entries(&batch, table_name, existing_item, &metadata)
+	if gsi_write_err != .None {
+		item_destroy(&existing_item)
+		if old, has := old_item.?; has {
+			old_copy := old
+			item_destroy(&old_copy)
+		}
+		return nil, nil, gsi_write_err
+	}
+
+	// Write batch atomically - ALL or NOTHING
+	write_err := rocksdb.batch_write(&engine.db, &batch)
+	if write_err != .None {
 		item_destroy(&existing_item)
 		if old, has := old_item.?; has {
 			old_copy := old
@@ -120,12 +158,6 @@ update_item :: proc(
 		return nil, nil, .RocksDB_Error
 	}
 
-	// --- GSI maintenance: delete old entries, write new entries ---
-	if old, has := old_item.?; has {
-		gsi_delete_entries(engine, table_name, old, &metadata)
-	}
-	gsi_write_entries(engine, table_name, existing_item, &metadata)
-
 	new_item = existing_item
 	return old_item, new_item, .None
-}
+}