Re: What does PostgreSQL do when time goes backward?

I wrote:
> How does PostgreSQL react to time being stepped at bootup? My Chrony
> NTP package might cause it to do so on rare occasions when the
> hardware clock is way off. This would only happen during bootup.

Ken writes:
> PostgreSQL does not use system time to track transactions so you
> should be good.

Thank you.

> Also, these types of clock changes by ntpd use the adjtime() system
> call which either slows or speeds the system clock to make the
> adjustment over a period of time so it should be minimally disruptive.

This is about Chrony <http://www.chrony.tuxfamily.org>, an alternative
ntp implementation. In any case, both chronyd and ntpd can step the
clock (possibly backwards) at bootup under some rare circumstances.

Frank writes:
> My ntp client changes clock (by small amount) at any time:
> Jul 25 05:29:38 bax ntpd[10269]: adjusting local clock by 0.098724s
> Jul 25 05:31:43 bax ntpd[10269]: adjusting local clock by 0.038991s
> Jul 25 06:13:38 bax ntpd[10269]: adjusting local clock by -0.037131s
> Jul 25 15:01:52 bax ntpd[10269]: adjusting local clock by -0.112429s

Ken writes:
> These do seem to be larger values than you might expect from a clock
> conditioned with ntpd. Is it a VM or is there something going on that
> would stop or suspend your system?

There is certainly something wrong there.
--
John Hasler
jhasler(at)newsguy(dot)com
Elmwood, WI USA