The database log is append only (with GC aterwards) so a one byte change on a large document re-writes the entire document. From https://rethinkdb.com/docs/dat

The database log is append only (with GC aterwards) so a one byte change on a large document re-writes the entire document. From https://rethinkdb.com/docs/data-modeling/ https://rethinkdb.com/docs/data-modeling/: Disadvantages of using embedded arrays: Deleting, adding or updating a post requires loading the entire posts array, modifying it, and writing the entire document back to disk. Because of the previous limitation, it’s best to keep the size of the posts array to no more than a few hundred documents.