Storage file size in distributed data lakes is optimized. At a first ingestion node of a plurality of ingestion nodes, a merge advisory is received from a coordinator. The merge advisory indicates a transaction identifier (ID). Received data associated with the transaction ID is persisted, which includes: determining whether the received data, persisted together in a single file will exceed a maximum desired file size; based on determining that the maximum desired file size will not be exceeded, persisting the received data in a single file; and based on determining that the maximum desired file size will be exceeded, persisting the received data in a plurality of files that each does not exceed the maximum desired file size. A location of the persisted received data in the permanent storage is identified, by the first ingestion node, to the coordinator.