Help Center/ GaussDB/ Feature Guide(Distributed_V2.0-3.x)/ Storage Engine/ Ustore/ Storage Format/ Index/ Row Consistency Read (RCR) UB-tree Multi-Version Management
Updated on 2025-08-22 GMT+08:00
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Row Consistency Read (RCR) UB-tree Multi-Version Management

  1. The UB-tree multi-version management adopts the key-based multi-version management. The latest version and historical versions are both on UB-tree.
  2. To save the space, xmin/xmax is expressed in xid-base + delta. The 64-bit xid-base is stored on pages and the 32-bit delta is stored on tuples. The xid-base on pages also needs to be maintained through additional logic.
  3. Keys are inserted into or deleted from the UB-tree in the sequence of key + TID. Tuples with the same index column are sorted based on their TIDs as the second keywords. The xmin and xmax are added to the end of the key.
  4. During index splitting, multi-version information is migrated with key migration.
Parent topic: Index