| From: | Thom Brown <thom(at)linux(dot)com> |
|---|---|
| To: | Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
| Subject: | Re: Freeze avoidance of very large table. |
| Date: | 2015-11-17 15:56:06 |
| Message-ID: | CAA-aLv7iRnht70WsXGOJuEk5CS_Khc77SmoiZNpGJng6NF8wDQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 17 November 2015 at 15:43, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:
> On 11/17/15 4:41 AM, Thom Brown wrote:
>>
>> Could someone post a TL;DR summary of what the current plan looks
>> like? I can see there is a huge amount of discussion to trawl back
>> through. I can see it's something to do with the visibility map. And
>> does it avoid freezing very large tables like the title originally
>> sought?
>
>
> Basically, it follows the same pattern that all-visible bits do, except
> instead of indicating a page is all-visible, the bit shows that all tuples
> on the page are frozen. That allows a scan_all vacuum to skip those pages.
So the visibility map is being repurposed? And if a row on a frozen
page is modified, what happens to the visibility of all other rows on
that page, as the bit will be set back to 0? I think I'm missing a
critical part of this functionality.
Thom
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