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Re: Experimental patch for inter-page delay in VACUUM

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jan Wieck <JanWieck(at)Yahoo(dot)com>
Cc: Ang Chin Han <angch(at)bytecraft(dot)com(dot)my>,Christopher Browne <cbbrowne(at)acm(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Experimental patch for inter-page delay in VACUUM
Date: 2003-11-04 15:58:46
Message-ID: 22408.1067961526@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> Tom Lane wrote:
>> I have never been happy with the fact that we use sync(2) at all.

> Sure does it do too much. But together with the other layer of 
> indirection, the virtual file descriptor pool, what is the exact 
> guaranteed behaviour of
>      write(); close(); open(); fsync();
> cross platform?

That isn't guaranteed, which is why we have to use sync() at the
moment.  To go over to fsync or O_SYNC we'd need more control over which
file descriptors are used to issue writes.  Which is why I was thinking
about moving the writes to a centralized writer process.

>> Actually, once you build it this way, you could make all writes
>> synchronous (open the files O_SYNC) so that there is never any need for
>> explicit fsync at checkpoint time.

> Yes, but then the configuration leans more towards "take over the RAM" 

Why?  The idea is to try to issue writes at a fairly steady rate, which
strikes me as much better than the current behavior.  I don't see why it
would force you to have large numbers of buffers available.  You'd want
a few thousand, no doubt, but that's not a large number.

			regards, tom lane

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Subject: Re: Experimental patch for inter-page delay in VACUUM
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