Re: Binary Replication and Slony

Much thanks to everyone! The mailing list, as usual, has been extremely
helpful.

On Mon, Sep 20, 2010 at 10:33 AM, Brad Nicholson
<bnichols(at)ca(dot)afilias(dot)info>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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--
---
John L Cheng