Guys, still need your help.
Previous night:
2019-04-05 00:35:04 UTC LOG: could not truncate directory "pg_serial": apparent wraparound
2019-04-05 00:40:04 UTC LOG: could not truncate directory "pg_serial": apparent wraparound
(2 checkpoints)
It turned that I have some problem with performance related to predicate locking on this platform.
A lot of long prepared statements with the SerializableXactHashLock and predicate_lock_manager wait_events followed by high CPU usage happened during 00:30 and 00:45. During this period there were 55k pred locks granted at max and 30k in average. Probably because of high CPU usage some statements were spending a lot of time in bind/parse steps.
Probably if you advise me what could cause "pg_serial": apparent wraparound messages I would have more chances to handle all the performance issues.
Thank you!
--
Pavel Suderevsky
пн, 11 мар. 2019 г. в 19:09, Pavel Suderevsky <psuderevsky@xxxxxxxxx>:
Hi,PG: 9.6.11OS: CentOSEnv: AWS EC2I've faced the following exceptions in PostgreSQL server log:> could not truncate directory "pg_serial": apparent wraparoundSometimes it repeats every 5 min and the longest period was 40 min.In fact, I can't find any suspicious events happening that periods.pg_wait_sampling didn't catch any events, no long queries (more than 60s), Autovacuum workers or transactions in "idle in transaction" state were in action at this time.The only related I could find in archive is: https://www.postgresql.org/message-id/CACjxUsON4Vya3a6r%3DubwmN-4qTDDfZjuwSzjnL1QjdUc8_gzLw%40mail.gmail.com>You should not see the errors you are reporting nor>the warning I mentioned unless a serializable transaction remains>active long enough for about 1 billion transaction IDs to be>consumed.Database age now is just 18.5 millions of transactions.Server has two standbys (sync and async), hot_standby_feedback is off.Please advice what I can do to find a reason of these exceptions.
