On 2024/07/10 2:57, Robert Haas wrote:
Here's v2.
Thanks for the patch! With v2 patch, I found a case where WAL data generated with wal_level = minimal is summarized. In the steps below, the hoge2_minimal table is created under wal_level = minimal, but its block modification information is included in the WAL summary files. I confirmed this by checking the contents of WAL summary files using pg_wal_summary_contents(). Additionally, the hoge3_replica table created under wal_level = replica is not summarized. ------------------------------------------- initdb -D data echo "wal_keep_size = '16GB'" >> data/postgresql.conf pg_ctl -D data start psql <<EOF SHOW wal_level; CREATE TABLE hoge1_replica AS SELECT n FROM generate_series(1, 100) n; ALTER SYSTEM SET max_wal_senders TO 0; ALTER SYSTEM SET wal_level TO 'minimal'; EOF pg_ctl -D data restart psql <<EOF SHOW wal_level; CREATE TABLE hoge2_minimal AS SELECT n FROM generate_series(1, 100) n; ALTER SYSTEM SET wal_level TO 'replica'; EOF pg_ctl -D data restart psql <<EOF SHOW wal_level; CREATE TABLE hoge3_replica AS SELECT n FROM generate_series(1, 100) n; CHECKPOINT; CREATE TABLE hoge4_replica AS SELECT n FROM generate_series(1, 100) n; CHECKPOINT; ALTER SYSTEM SET summarize_wal TO on; SELECT pg_reload_conf(); SELECT pg_sleep(5); SELECT wsc.*, c.relname FROM pg_available_wal_summaries() JOIN LATERAL pg_wal_summary_contents(tli, start_lsn, end_lsn) wsc ON true JOIN pg_class c ON wsc.relfilenode = c.relfilenode WHERE c.relname LIKE 'hoge%' ORDER BY c.relname; EOF ------------------------------------------- I believe this issue occurs when the server is shut down cleanly. The shutdown-checkpoint record retains the wal_level value used before the shutdown. If wal_level is changed after this, the wal_level that indicated by the shutdown-checkpoint record and that the WAL data generated afterwards depends on may not match. I'm sure this patch is necessary as a safeguard for WAL summarization. OTOH, I also think we should apply the patch I proposed earlier in this thread, which prevents summarize_wal from being enabled when wal_level is set to minimal. This way, if there's a misconfiguration, users will see an error message and can quickly identify and fix the issue. Thought? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
