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Re: making use of large TLB pages

From: Neil Conway <neilc(at)samurai(dot)com>
To: "Jonah H(dot) Harris" <jharris(at)nightstarcorporation(dot)com>
Cc: "'Bruce Momjian'" <pgman(at)candle(dot)pha(dot)pa(dot)us>,"'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>,"'PostgreSQL Hackers'" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: making use of large TLB pages
Date: 2002-09-30 03:03:52
Message-ID: 87lm5kgovb.fsf@mailbox.samurai.com (view raw or flat)
Thread:
Lists: pgsql-hackers
"Jonah H. Harris" <jharris(at)nightstarcorporation(dot)com> writes:
> I agree with Bruce and Tom.

AFAIK Bruce and Tom (and myself) agree that this is a good idea,
provided it makes a noticeable performance difference (and if it
doesn't, it's not worth applying).

>  AFAIK and in my experience I don't think it will be a significantly
> measurable increase.

Can you elaborate on this experience?
  
> Not only that, but the portability issue itself tends to make it
> less desireable.

Well, that's obvious: code that improves PostgreSQL on *all* platforms
is clearly superior to code that only improves it on a couple. That's
not to say that the latter code is absolutely without merit, however.

> Sorry if my comments are out-of-line on this one but it has been a
> thread for some time I'm just kinda tired of reading theory vs
> proof.

Well, ISTM the easiest way to get some "proof" is to implement it and
benchmark the results. IMHO any claims about performance prior to that
are mostly hand waving.

> Since you are so set on trying to implement this, I'm just wondering
> what documentation has tested evidence of measurable increases in
> similar situations?

(/me wonders if people bother reading the threads they reply to)

http://lwn.net/Articles/10293/

According to the HP guys, Oracle saw an 8% performance improvement in
TPC-C when they started using large pages.

To be perfectly honest, I really have no idea if that will translate
into an 8% performance gain for PostgreSQL, or whether the performance
gain only applies if you're using a machine with 16GB of RAM, or
whether the speedup from large pages is really just a correction of
some Oracle deficiency that we don't suffer from, etc. However, I do
think it's worth finding out.

Cheers,

Neil

-- 
Neil Conway <neilc(at)samurai(dot)com> || PGP Key ID: DB3C29FC


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