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Re: Synchronous replication & Hot standby patches

From: Hannu Krosing <hannu(at)2ndQuadrant(dot)com>
To: jd(at)commandprompt(dot)com
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, "K, Niranjan (NSN - IN/Bangalore)" <niranjan(dot)k(at)nsn(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Synchronous replication & Hot standby patches
Date: 2009-02-27 20:17:36
Message-ID: 1235765856.7189.6.camel@huvostro (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 2009-02-24 at 10:34 -0800, Joshua D. Drake wrote:
> On Tue, 2009-02-24 at 17:36 +0000, Simon Riggs wrote:
> > On Wed, 2009-02-25 at 00:51 +0900, Fujii Masao wrote:
> > 
> > > On Tue, Feb 24, 2009 at 3:47 PM, K, Niranjan (NSN - IN/Bangalore)
> > > <niranjan(dot)k(at)nsn(dot)com> wrote:
> > > > Could you please let me know what are the outstanding features that are still to be developed in the respective patches?
> > > >
> > > > I'am currently referring the wiki: "Todo and Claim" for NTT and for HotStandby, i see that almost all issues are closed. Are there any features / refactoring / bugs still need to be fixed.
> > > 
> > > At least I'm planning to work on the following two items of Synch Rep for v8.5.
> > > Of course, Synch Rep works fine without these features.
> > 
> > > - Add new feature which transfers all WAL records via the direct connection
> > >   between the primary and the standby. In other words, get rid of
> > >   file-based log shipping part from the patch.
> > >   http://archives.postgresql.org/message-id/496B9495.4010902@enterprisedb.com
> > 
> > Please bear in mind my strong objection to this. Attempting to transfer
> > all data via a single connection destroys VLDB usage of this feature. So
> > for me its just additional code for ease-of-use in the simplest case,
> > not code replacement.
> 
> Well VLDB is like 2% of what we need. If the above will remove all the
> B.S. currently associated with actually doing PITR (rsync, scp, nfs,
> pg_standby pick your poison) then I am all for it.

If you use walmgr.py, then all you need is writing a conf file and
making sure that ssh and rsync work.

Actually the best way to do Sync Rep would have been to just move to C
what walmgr.py does. That the patch could have started off from a
well-tested foundation.

> Log shipping should be:
> 
> I am master, my slave is here.
> I am slave, I understand my master is here.
> Here is our mutual authentication love token.
> Let congress begin.
> 
> Anything more and we are being difficult for the sake of being
> difficult.

Actually I'd leave out the first line, and start with just

- I am slave, my master accepts me, start replicationg

So there could be several slaves, of both hot standby postgresql,
wal-file-store and store-and-forward-to-many types.


-- 
Hannu Krosing   http://www.2ndQuadrant.com
PostgreSQL Scalability and Availability 
   Services, Consulting and Training


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Subject: Re: Synchronous replication & Hot standby patches
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