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Re: Dynamic Partitioning using Segment Visibility Maps

From: Markus Schiltknecht <markus(at)bluegap(dot)ch>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Andrew Sullivan <ajs(at)crankycanuck(dot)ca>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Dynamic Partitioning using Segment Visibility Maps
Date: 2008-01-04 21:26:54
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Lists: pgsql-hackers

Simon Riggs wrote:
> On Fri, 2008-01-04 at 13:06 -0500, Andrew Sullivan wrote:
>> On Fri, Jan 04, 2008 at 01:29:55PM +0100, Markus Schiltknecht wrote:
>>> Agreed. Just a minor note: I find "marked read-only" too strong, as it 
>>> implies an impossibility to write. I propose speaking about mostly-read 
>>> segments, or optimized for reading or similar.

Hm.. yeah, after rereading, I realize that I've mixed up states no. 2 
and 3 here, sorry.

>> I do want some segments to be _marked_ read-only: I want attempted writes to
>> them to _fail_.

Well, I can see use cases for marking tuples or complete relations as 
read only. But segments?

I'm still puzzled about how a DBA is expected to figure out which 
segments to mark. Simon, are you assuming we are going to pass on 
segment numbers to the DBA one day?

If not, a more user friendly command like "MARK READ ONLY WHERE date <= 
2006" would have to move tuples around between segments, so as to be 
able to satisfy the split point exactly, right?

> I think Markus thought that we would mark them read only automatically,
> which was not my intention. I believe its possible to have this in a way
> that will make you both happy. Some more explanation:
> There would be three different states for a segment:
> 1. read write
> 2. "optimized for reading", as Markus says it
> 3. marked read only by explicit command

Thanks for clarification.



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