Abstract: Techniques for fast online scaling of a database via a split architecture including decoupled storage and compute tiers in a database service are described. A cluster of database (DB) nodes is scaled to add a new DB node. The scaling includes determining a split for data of a first volume managed by an existing DB node. A second DB node is obtained, and the first volume is cloned according to a lightweight copy technique to yield a second volume for use by the second DB node. After the cloning, a set of database modifications are applied to the second volume based on modifications caused by database traffic received by the first DB node, involving the the volume, during the cloning of the first volume. Each DB node may drop the portion of the volume that it does not need according to the split.