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Re: ice-broker scan thread

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: "Pollard, Mike" <mpollard(at)cincom(dot)com>
Cc: Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: ice-broker scan thread
Date: 2005-11-29 15:06:18
Message-ID: 20051129150617.GE31333@svana.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Nov 29, 2005 at 09:45:30AM -0500, Pollard, Mike wrote:
> Anyway, what I did was the following.  When doing a sequential scan, we
> were starting at the beginning of the table and scanning forward.  If I
> threw up some threads to read ahead, then my user thread and my read
> ahead threads would thrash on trying to lock the buffer slots.  So, I

<snip>

> so above, the user threads is starting low in the table and working
> high; the readahead threads are starting higher (but not at the end of
> the table), and working low.  

Ok, this may be a really dumb question, but doesn't this rely on the
fact that the table is smaller than the amount of buffers? If the table
is large most of your data will be tossed out again by later data
before it's been used by the backend.

Have a nice day,
-- 
Martijn van Oosterhout   <kleptog(at)svana(dot)org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

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