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Re: [HACKERS] ERROR: could not read block

From: "Magnus Hagander" <mha(at)sollentuna(dot)net>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>,<tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <zhouqq(at)cs(dot)toronto(dot)edu>, <icub3d(at)gmail(dot)com>,<pgsql-admin(at)postgresql(dot)org>, <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] ERROR: could not read block
Date: 2005-11-17 18:56:21
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-adminpgsql-hackers
> >>> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>  >>>
> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> > None of this seems material, however.  It's pretty clear that the 
> > problem was exhaustion of the Windows page pool.
> > ...
> > If we don't want to tell Windows users to make highly technical 
> > changes to the Windows registry in order to use PostgreSQL, it does 
> > seem wise to use retries, as has already been discussed on this 
> > thread.
> Would a simple retry loop actually help?  It's not clear to 
> me how persistent such a failure would be.

(Not sure why I didn't get Toms mail - lists acting up again? Anyway, I
got Kevins response, but am responding primarily to Tom)

The way I read it, a delay should help. It's basically running out of
kernel buffers, and we just delay, somebody else (another process, or an
IRQ handler, or whatever) should get finished with their I/O, free up
the buffer, and let us have it. Looking around a bit I see several
references that you should retry on it, but nothing in the API docs.
I do think it's probably a good idea to do a short delay before retrying
- at least to yield the CPU for one slice. That would greatly increase
the probability of someone else finishing their I/O...

That's how I read it, but I'm not 100% sure.



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