Обсуждение: Time slowly goes out of sync Cygwin+windows+psotgres

Running postgres on cygwin and windows.

Cygwin has the correct time.
Windows has the same time as cygwin.

Postgres slowly goes out of sync.  Over a month it ends up 10 minutes out.

using e.g. "SELECT NOW()";

restart the machine and posgres is only 30 seconds out.

Is postgres calculateing the time itself or reading of the machines clock?

Is there a setting to make it go off the operating system clock?

Aaron <aarmel@netagi.com> writes:
> Is postgres calculateing the time itself or reading of the machines clock?

Postgres just asks the OS what time it is.  I think you have an
off-speed system clock crystal (lots of PC-grade hardware will
gain or lose 10 minutes/month :-().

I don't know what test you are using to convince yourself that the OS
time is correct when Postgres' time is different --- but I'll bet lunch
you made a mistake.

One other thing to watch for is that "SELECT now()" returns the time as
of the start of the current transaction.  If you said "begin" and then
waited ten minutes you could get a 10-minute discrepancy.  I doubt you
did that, but it's something to be aware of.

            regards, tom lane

On Fri, 23 Aug 2002, Aaron wrote:

> Running postgres on cygwin and windows.
>
> Cygwin has the correct time.
> Windows has the same time as cygwin.
>
> Postgres slowly goes out of sync.  Over a month it ends up 10 minutes out.
>
> using e.g. "SELECT NOW()";

It might be possible that time() and gettimeofday() are returning
different times, we use the latter, I'd guess that what you're using
to get the date may use the former if it only gives integral seconds.

At 10:14 AM 8/29/02 -0400, Tom Lane wrote:
>Postgres just asks the OS what time it is.  I think you have an off-speed
>system clock crystal (lots of PC-grade hardware will gain or lose 10
>minutes/month :-().

On the other hand, in a day of Network Time Protocol (NTP) there is
absolutely no excuse for a machine to have a date/time off by more than a
few milliseconds.

UNIX users probably already have an ntpd available on their system, if not
it's an easy download.

On my windows boxes I use "Dimension 4" http://www.thinkman.com/~thinkman
for a free sntp agent.



         -crl
--
Chad R. Larson (CRL22)    chad@eldocomp.com
   Eldorado Computing, Inc.   602-604-3100
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