Help Center/ Document Database Service/ FAQs/ Resource and Disk Management/ Why Does Available Disk Space Not Increase After Data Is Deleted?
Updated on 2026-06-23 GMT+08:00
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Why Does Available Disk Space Not Increase After Data Is Deleted?

  • Regardless of whether the operation is an insert, update, or delete (including index insertions and deletions), all operations are ultimately converted into writes in the background. Deleting data of an instance in use does not reclaim disk space. The unreclaimed space is referred to as disk fragments. The database continues to reuse this fragmented space, meaning that new data can be written into these fragments without allocating additional disk space. The specific behavior varies depending on the underlying storage engine (RocksDB or WiredTiger).
  • In RocksDB, delete operations are internally converted into append writes. After accumulating a certain amount of redundant data, RocksDB automatically triggers background compact threads to merge multiple versions of the same data and release unnecessary disk space. Therefore, you are advised to wait for the system to reclaim space automatically. When disk usage becomes high and approaches the read-only threshold, submit a service ticket.
  • In WiredTiger, after data is deleted and multi-version records are merged during compaction, disk space fragments are also generated. However, WiredTiger does not return this space to the OS. Instead, it marks the space as reserved for future writes of the current collection. Subsequent writes to this collection will preferentially reuse this reserved space. If you need to release this portion of disk space, you can run the compact command. (This command blocks normal operations, so it is disabled by default.)
Parent Topic: Resource and Disk Management