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Re: draft RFC: concept for partial, wal-based replication

From: Hans-Jürgen Schönig <hs(at)cybertec(dot)at>
To: Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>
Cc: Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org, Itagaki Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Boszormenyi Zoltan <zb(at)cybertec(dot)at>
Subject: Re: draft RFC: concept for partial, wal-based replication
Date: 2009-11-30 16:46:45
Message-ID: 229F4CC7-BAC2-42BC-9D67-C1A1877F6F9E@cybertec.at (view raw or flat)
Thread:
Lists: pgsql-hackers
On Nov 30, 2009, at 10:32 AM, Stefan Kaltenbrunner wrote:

> Andres Freund wrote:
>> On Monday 30 November 2009 03:57:11 Itagaki Takahiro wrote:
>>> Boszormenyi Zoltan <zb(at)cybertec(dot)at> wrote:
>>>> we tried to discuss on a lower level what should be needed
>>>> for a partial replication based on streaming replication.
>>> We need to discuss a "partial recovery" before the partial  
>>> replication.
>> If you do the filtering on the sending side you dont actually need  
>> partial recover in the sense that you filter in the rmgr or similar.
>> Or do I miss something?
>
> the question is if filtering on the sending side is actually the  
> "right thing" to do.
> It increases the overhead and the complexity on the master,  
> especially if you think about different (partial) replication  
> agreements for different slaves and it might also be hard to  
> integrate with the planned sync/async modes.
> On the other hand if you filter on the master you might be able to  
> avoid a lot of network traffic du to filtered wal records.
> I think for a first step it might make more sense to look into doing  
> the filtering on the receiving side and look into actual integration  
> with SR at a later stage.
>
>
> Stefan


hello ...

one problem with not-filtering on the master is that you will end up  
with a lot of complexity if you start adding new tables to a replica  
because you just cannot add tables as easy as when you are doing stuff  
on the slave. the procedure seems ways more complex.
in addition to that you are sending WAL which has to be discarded  
anyway.
we thought about filtering "outside the master" a lot but to me it did  
not sound like good plan.

	regards,

		hans


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