From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Martin Pihlak <martin(dot)pihlak(at)gmail(dot)com> |
Cc: | Magnus Hagander <magnus(at)hagander(dot)net>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: reducing statistics write overhead |
Date: | 2008-09-07 19:52:47 |
Message-ID: | 28445.1220817167@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Martin Pihlak <martin(dot)pihlak(at)gmail(dot)com> writes:
> I had also previously experimented with stat() based polling but ran into
> the same issues - no portable high resolution timestamp on files. I guess
> stat() is unusable unless we can live with 1 second update interval for the
> stats (eg. backend reads the file if it is within 1 second of the request).
> One alternative is to include a timestamp in the stats file header - the
> backend can then wait on that -- check the timestamp, sleep, resend the
> request, loop. Not particularly elegant, but easy to implement. Would this
> be acceptable?
Timestamp within the file is certainly better than trying to rely on
filesystem timestamps. I doubt 1 sec resolution is good enough, and
I'd also be worried about issues like clock skew between the
postmaster's time and the filesystem's time.
regards, tom lane
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