On 2020/07/09 11:36, osumi.takami...@fujitsu.com wrote:
Hello, hackers. I've been thinking to suggest a peformance-oriented feature for COPY FROM. It's UNLOGGED clause, which means data loading skipping WAL generation.
This feature can work safely with wal_level=replica or logical? Or it can work only with wal_level=minimal? If yes, what is the main difference between this method and wal_skip_threshold?
How to make it work is the following. 1. Aquire ACCESS EXCLUSIVE mode to lock the target table and its indexes. 2. Mark those relations 'unrecoverable' in pg_class/pg_index. 3. Issue one WAL to indicate when COPY UNLOGGED is executed. 4. Execute the data loading, bypassing WAL generation for data. 5. Sync the data to disk by performing checkpoint.
What happens if the server crashes before #5? Since no WAL for data-loading can be replayed, the target table should be truncated? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
