Sunday, September 7, 2008

Re: [HACKERS] reducing statistics write overhead

Magnus Hagander wrote:
> I wrote a patch for this some time back, that was actually applied.
> Turns out it didn't work, and I ran out of time to fix it, so it was
> backed out again. And then I forgot about it :-) If you look through the
> cvs history of pgstat you should be able to find it - maybe it can give
> you some further ideas.

Got it - this was 1.126. Looks very familiar indeed :)

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?


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