From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201102012021.p11KLWC19481@momjian.us>
Subject: Re: [GENERAL] Binary Replication and Slony
In-Reply-To: <4C979AEF.9030402@ca.afilias.info>
To: Brad Nicholson <bnichols@ca.afilias.info>
Date: Tue, 1 Feb 2011 15:21:31 -0500 (EST)
CC: PostgreSQL-documentation <pgsql-docs@postgresql.org>
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I have applied the attached documentation improvement to better
highlight Slony's abilities.

---------------------------------------------------------------------------

Brad Nicholson wrote:
>   On 10-09-20 12:49 PM, Bruce Momjian wrote:
> > John Cheng wrote:
> >> Congrats on the 9.0 release of PostgreSQL. One of the features I am really
> >> interested in is the built-in binary replication.
> >>
> >> Our production environment has been using PostgreSQL for more than 5 years
> >> (since this project started). We have been using Slony-I as our replication
> >> mechanism. I am interested to find out the pros and cons of Slony vs the
> >> built-in replication in 9.0. Based on what I understand:
> >>
> >> * Slony has a higher overhead than the binary replication in 9.0
> >> * When using Slony, schema change must be applied via slonik (in most cases)
> >> * Unfortunately, IMO it is easy to make a mistake when applying schema
> >> changes in Slony, fortunately, it is easy to drop and recreate the
> >> replication sets
> >> * Slony is an asynchronous replication mechanism
> >> * Slony allows you to replication some tables, while ignoring others
> >>
> >> * PostgreSQL 9.0 with hot standby&  streaming replication is an asynchronous
> >> replication mechanism
> >> * Overhead is low compared to Slony
> >>
> >> Are there some cases where it is better to use Slony, for example, when you
> >> must specifically exclude tables from replication? I believe our system will
> >> be better off using the built-in replication mechanism of 9.0, and I am
> >> guessing most people will be in the same boat.
> > You have summarized the differences well.  Streaming replication has
> > lower overhread, but doesn't allow per-table granularity or allow
> > replication between different versions of Postgres.
> >
> 
> Slony will also allow you to:
> 
> -run custom schema (like extra indexes) on replicas
> -replicate between different hardware architectures and OS's
> -run lengthy queries against replicas having to worry about trade offs 
> surrounding query cancellation vs standby lagging.
> -switch roles of two nodes without entering a degraded state or worrying 
> about STONITH.  If you switch roles in a controlled manner, both nodes 
> remain in the cluster.  Slony prevents writes against the replica.
> 
> I do agree that for most, Slony is overkill and streaming replication 
> and hot standby will be the better choice.
> 
> -- 
> Brad Nicholson  416-673-4106
> Database Administrator, Afilias Canada Corp.
> 
> 
> 
> -- 
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-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

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diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 4f59fd1..226d616 100644
*** a/doc/src/sgml/runtime.sgml
--- b/doc/src/sgml/runtime.sgml
*************** pg_dumpall -p 5432 | psql -d postgres -p
*** 1704,1709 ****
--- 1704,1711 ----
     <para>
      It is also possible to use certain replication methods, such as
      <productname>Slony</>, to create a standby server with the updated version of
+     <productname>PostgreSQL</>.  This is possible because Slony supports
+     replication between different major versions of
      <productname>PostgreSQL</>.  The standby can be on the same computer or
      a different computer.  Once it has synced up with the master server
      (running the older version of <productname>PostgreSQL</>), you can

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