From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>, 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: | 2015-04-24 11:52:04 |
Message-ID: | CA+TgmoYuZQoZPB4+8fppsU4M=JrhvWU5u8HHc1RHV50s3zujYg@mail.gmail.com |
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On Thu, Apr 23, 2015 at 9:03 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Thu, Apr 23, 2015 at 10:42 PM, Robert Haas wrote:
>> On Thu, Apr 23, 2015 at 4:19 AM, Simon Riggs wrote:
>>> We only need a freeze/backup map for larger relations. So if we map 1000
>>> blocks per map page, we skip having a map at all when size < 1000.
>>
>> Agreed. We might also want to map multiple blocks per map slot - e.g.
>> one slot per 32 blocks. That would keep the map quite small even for
>> very large relations, and would not compromise efficiency that much
>> since reading 256kB sequentially probably takes only a little longer
>> than reading 8kB.
>>
>> I think the idea of integrating the freeze map into the VM fork is
>> also worth considering. Then, the incremental backup map could be
>> optional; if you don't want incremental backup, you can shut it off
>> and have less overhead.
>
> When I read that I think about something configurable at
> relation-level.There are cases where you may want to have more
> granularity of this information at block level by having the VM slots
> to track less blocks than 32, and vice-versa.
What are those cases? To me that sounds like making things
complicated to no obvious benefit.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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