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Re: Core team statement on replication in PostgreSQL

From: Andreas 'ads' Scherbaum <adsmail(at)wars-nicht(dot)de>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-05-30 22:47:19
Message-ID: 20080531004719.4b8206a0@iridium.wars-nicht.de (view raw or flat)
Thread:
Lists: pgsql-advocacypgsql-hackers
On Fri, 30 May 2008 17:05:57 -0400 Andrew Dunstan wrote:
> Andreas 'ads' Scherbaum wrote:
> > On Thu, 29 May 2008 23:02:56 -0400 Andrew Dunstan wrote:
> >
> >> Well, yes, but you do know about archive_timeout, right? No need to wait 
> >> 2 hours.
> >
> > Then you ship 16 MB binary stuff every 30 second or every minute but
> > you only have some kbyte real data in the logfile. This must be taken
> > into account, especially if you ship the logfile over the internet
> > (means: no high-speed connection, maybe even pay-per-traffic) to the
> > slave.
> 
> Sure there's a price to pay. But that doesn't mean the facility doesn't 
> exist. And I rather suspect that most of Josh's customers aren't too 
> concerned about traffic charges or affected by such bandwidth 
> restrictions. Certainly, none of my clients are, and they aren't in the 
> giant class. Shipping a 16Mb file, particularly if compressed, every 
> minute or so, is not such a huge problem for a great many commercial 
> users, and even many domestic users.

The real problem is not the 16 MB, the problem is: you can't compress
this file. If the logfile is rotated it still contains all the
old binary data which is not a good starter for compression.

So you may have some kB changes in the wal logfile every minute but you
still copy 16 MB data. Sure, it's not so much - but if you rotate a
logfile every minute this still transfers 16*60*24 = ~23 GB a day.


Kind regards

-- 
				Andreas 'ads' Scherbaum
German PostgreSQL User Group

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