Help Center/ GaussDB/ Centralized_3.x/ Storage Engine/ Ustore/ Overview
Updated on 2024-07-04 GMT+08:00
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Overview

Ustore is an in-place update storage engine launched by GaussDB. The biggest difference between Ustore and Astore lies in that, the latest data and historical data (excluding indexes) are stored separately. Now, Ustore is a default row-store engine of GaussDB.

Ustore Advantages

  1. The latest data and historical data are stored separately. Compared with Astore, Ustore has a smaller scanning scope. The HOT chain of Astore is removed. Non-index columns, index columns, and heaps can be updated in-place without change to row IDs. Historical data can be recycled in batches, which is friendly to the expansion of the latest data.
  2. If the same row is updated in a large concurrency, the in-place update mechanism of Ustore ensures the stability of tuple row IDs and update latency.
  3. VACUUM is not the only way to clear historical data. Indexes are decoupled from heaps and can be cleared separately with good I/O stability.
  4. The flashback function is supported.

However, in addition to modifying data pages, Ustore DML operations also modify undo logs. Therefore, the update overhead is higher. In addition, the scanning overhead of a single tuple is high because of replication (Astore returns pointers).