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Re: Proof-of-concept ARC removal patches

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Proof-of-concept ARC removal patches
Date: 2005-02-04 17:57:07
Message-ID: 15713.1107539827@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> The use of 25% T1 and 75% T2 is probably the only thing to discuss, for
> me.

Hmm.  I had been trying to avoid adding a GUC parameter for this ;-)

> A default setting of something like T1 as % of total (just roughly)
> = 50% when shared_buffers <= 1000
> = 25% when shared_buffers = 5000
> = 10% when shared_buffers = 20000
> with smoothing...

Have you got anything to back up the need for such an adjustment?

BTW, now that I look at this code more closely, I'm feeling dissatisfied
with Jan's custom adjustments to the ARC algorithm, particularly the
rule that it takes touches from two different transactions to get a page
into T2.  I preserved that logic in these proposed patches but I'm
thinking that we want to change it, independently of the ARC/2Q issue.
I'll start another thread in pghackers about that.  I bring it up now
just because I think that it has an impact on the desirable size of T1.
It might be unwise to put too much emphasis on comparative benchmarks
taken before we change that rule.

			regards, tom lane

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