Re: Vacuum: allow usage of more than 1GB of work mem

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Vacuum: allow usage of more than 1GB of work mem
Date: 2016-11-17 21:54:55
Message-ID: CAGTBQpbZX5S4QrnB6YP-2Nk+A9bxbaVktzKwsGvMeov3MTgdiQ@mail.gmail.com
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On Thu, Nov 17, 2016 at 6:34 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Nov 17, 2016 at 1:42 PM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
>> Attached is patch 0002 with pgindent applied over it
>>
>> I don't think there's any other formatting issue, but feel free to
>> point a finger to it if I missed any
>
> Hmm, I had imagined making all of the segments the same size rather
> than having the size grow exponentially. The whole point of this is
> to save memory, and even in the worst case you don't end up with that
> many segments as long as you pick a reasonable base size (e.g. 64MB).

Wastage is bound by a fraction of the total required RAM, that is,
it's proportional to the amount of required RAM, not the amount
allocated. So it should still be fine, and the exponential strategy
should improve lookup performance considerably.

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