| From: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(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: | 2016-09-16 04:52:22 |
| Message-ID: | CABOikdMzm_jupTigw+8ksfTVCS3QOP_FW3sG15050km3nZbtSw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Sep 16, 2016 at 9:09 AM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
wrote:
>
> I also realised that we can compact the TID array in step (b) above
> because we only need to store 17 bits for block numbers (we already know
> which 1GB segment they belong to). Given that usable offsets are also just
> 13 bits, TID array needs only 4 bytes per TID instead of 6.
>
>
Actually this seems like a clear savings of at least 30% for all use cases,
at the cost of allocating in smaller chunks and doing some transformations.
But given the problem we are trying to solve, seems like a small price to
pay.
Thanks,
Pavan
--
Pavan Deolasee http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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