From: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
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To: | david(dot)rowley(at)2ndquadrant(dot)com |
Cc: | kommi(dot)haribabu(at)gmail(dot)com, thomas(dot)munro(at)enterprisedb(dot)com, andres(at)anarazel(dot)de, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Accounting of zero-filled buffers in EXPLAIN (BUFFERS) |
Date: | 2018-11-15 06:31:02 |
Message-ID: | 20181115.153102.145796999.horiguchi.kyotaro@lab.ntt.co.jp |
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Lists: | pgsql-hackers |
At Thu, 12 Jul 2018 10:31:46 +1200, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> wrote in <CAEepm=2yGnw6dJ5wx8tuSRmcpDZ5uziiH_qQ0ptdha8mMLSVqw(at)mail(dot)gmail(dot)com>
> I suppose someone might argue that even when it's not a hit and it's
> not a read, we might still want to count this buffer interaction in
> some other way. Perhaps there should be a separate counter? It may
> technically be a kind of cache miss, but it's nowhere near as
> expensive as a synchronous system call like read() so I didn't propose
> that.
At Thu, 12 Jul 2018 10:19:29 +1000, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> wrote in <CAJrrPGduEpxwtu9VFxT21DNK=WRP=LUjK4GjPfm+4+PCjpcAxA(at)mail(dot)gmail(dot)com>
> Thanks for the details. I got your point. But we need to include
> RBM_ZERO_ON_ERROR case read operations, excluding others
> are fine.
FWIW I agree to Haribabu's comment that the case of RBM_ZERO_*
other than ON_ERROR is a hit. It seems to show zheap's disk I /O
reduction by itself in certain extent.
At Thu, 12 Jul 2018 13:28:37 +1200, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote in <CAKJS1f_kem=OzVpFADzC2=VpzcXuSQ+HCW=Hp67GAXrnQ-EVTw(at)mail(dot)gmail(dot)com>
> On 12 July 2018 at 12:19, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> wrote:
> > Yes, I agree that we may need a new counter that counts the buffers that
> > are just allocated (no read or no write). But currently, may be the counter
> > value is very less, so people are not interested.
> The existing counters don't show up in EXPLAIN (ANALYZE, BUFFERS) when
> they're zero. The new counter would surely work the same way, so the
> users wouldn't be burdened by additional explain output it when
> they're not affected by it.
I don't object strongly neither to the new counter but I'm not
sure it is enough distinctive from hits, in the view that "a hit
is where we found a buffer for the requested page".
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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