On Sat, 16 Sep 2006, Manuel V?zquez Acosta wrote:

I've done it recently.
I don't have access to my notes or any of the config files at the moment but 
can probably send you more details during the week.


It involves:

-Setting up slony as per normal with a master and a slave
-Setting up heartbeat to use a virtual IP on the master that your 
applications will use when they want to connect to the database.
-Writing a script in heatbeat's resource.d that gets called on heart beat 
start events for slony.

The script I wrote supported start and status operations.
For the start operation it had two modes

1) A controlled switch over mode that I activated with a touch file in /tmp. 
This mode  did a MOVE SET, and was for promoting the slave when the master 
was still running (ie in preparation for taking the master down for 
maintenance).
2) A fail over mode that would execute if heartbeat on the slave detected that 
the master went away.

The script also had a status command that would return if the database on 
the local host was the origin for the slony replication set.

You also want to make sure that the auto_failback (It might be named 
something different) is turned off so IF the primary does come back online 
heartbeat does not try to make it the master again.

We took the approach that if the system did a fail over then the master was 
dropped from the replication set and if it did come back online it would not 
get automatically added back as a slony slave.   The system would run 
without a second database until someone manually re-provisioned the primary 
server as a new slony slave.


As Andrew indicated, if your primary server goes down and the secondary 
becomes the master then any data on the primary that hadn't yet made it to 
the secondary server at time of failover might be lost.   You would still be 
able to access the database on the primary server (Once you fix whatever 
went wrong in the first place) but slony won't be able to send the 
unreplicated data out.

I don't have any experiences with failures in a production enviornment to 
say how well it works.



Steve

> Hi all,
>
> I'm trying to set up a Active/Pasive configuration for PostgreSQL
> using Slony and Heartbeat.
>
> I'm wondering if anyone has done it before, and give some ideas.
>
> Best regards
> Manuel.
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