WAL replay is too slow on secondary server
| От | OMPRAKASH SAHU |
|---|---|
| Тема | WAL replay is too slow on secondary server |
| Дата | |
| Msg-id | CAOZWJqPc+s_vA-UfWWLR0s6Mt+DCffjXXVyLHJNJiuMrDLTYcA@mail.gmail.com обсуждение исходный текст |
| Ответы |
Re: WAL replay is too slow on secondary server
Re: WAL replay is too slow on secondary server |
| Список | pgsql-admin |
Hi Team,
Greetings!!
We have a postgresql cluster setup using patroni.
The DB is being used for heavy transactional application, now the problem is that on replica server WAL replay is too slow.
We have increased the IOPS to 6k and Throughput to 600 on nvme EBS volume of wal directory and 10k &800 on data directory.
but the WAL is being accumulated on the replica as usual and applying wal is having no improvement.
changed the maintenance_io_concurrency on replica to 32.
CPU utilization max=20% , RAM utilization is also max 20.
see the below postgres logs that shows around 2hrs lag
tail -f /var/log/postgresql/postgresql.log
2025-10-30 09:02:08 IST [27125]: user=,db=,app=,client=LOG: recovery restart point at 5B65/F1DAFA20
2025-10-30 09:02:08 IST [27125]: user=,db=,app=,client=DETAIL: Last completed transaction was at log time 2025-10-30 07:16:40.115131+05:30.
2025-10-30 09:08:23 IST [27125]: user=,db=,app=,client=LOG: restartpoint starting: time
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=LOG: restartpoint complete: wrote 44067 buffers (2.1%); 1 WAL file(s) added, 73 removed, 0 recycled; write=269.362 s, sync=0.042 s, total=269.633 s; sync files=142, longest=0.005 s, average=0.001 s; distance=1197052 kB, estimate=1587336 kB; lsn=5B66/6C3082F8, redo lsn=5B66/3AEAEA60
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=LOG: recovery restart point at 5B66/3AEAEA60
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=DETAIL: Last completed transaction was at log time 2025-10-30 07:21:47.56674+05:30.
2025-10-30 09:02:08 IST [27125]: user=,db=,app=,client=LOG: recovery restart point at 5B65/F1DAFA20
2025-10-30 09:02:08 IST [27125]: user=,db=,app=,client=DETAIL: Last completed transaction was at log time 2025-10-30 07:16:40.115131+05:30.
2025-10-30 09:08:23 IST [27125]: user=,db=,app=,client=LOG: restartpoint starting: time
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=LOG: restartpoint complete: wrote 44067 buffers (2.1%); 1 WAL file(s) added, 73 removed, 0 recycled; write=269.362 s, sync=0.042 s, total=269.633 s; sync files=142, longest=0.005 s, average=0.001 s; distance=1197052 kB, estimate=1587336 kB; lsn=5B66/6C3082F8, redo lsn=5B66/3AEAEA60
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=LOG: recovery restart point at 5B66/3AEAEA60
2025-10-30 09:12:53 IST [27125]: user=,db=,app=,client=DETAIL: Last completed transaction was at log time 2025-10-30 07:21:47.56674+05:30.
recovery_prefetch output:
postgres=# select * from pg_stat_recovery_prefetch;
stats_reset | prefetch | hit | skip_init | skip_new | skip_fpw | skip_rep | wal_distance | block_distance | io_depth
----------------------------------+----------+-----------+-----------+----------+----------+-----------+--------------+----------------+----------
2025-10-29 23:02:21.396179+05:30 | 182762 | 251000856 | 3841721 | 1100099 | 3520777 | 137392573 | 8984 | 80 | 0
(1 row)
stats_reset | prefetch | hit | skip_init | skip_new | skip_fpw | skip_rep | wal_distance | block_distance | io_depth
----------------------------------+----------+-----------+-----------+----------+----------+-----------+--------------+----------------+----------
2025-10-29 23:02:21.396179+05:30 | 182762 | 251000856 | 3841721 | 1100099 | 3520777 | 137392573 | 8984 | 80 | 0
(1 row)
I would request your thoughts and suggestions if we can get rid of this slowness and get some speed.
Regards,
OM
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