On Wed, Nov 18, 2009 at 08:40:14AM -0500, Andrew Sullivan wrote:
- On Tue, Nov 17, 2009 at 04:15:29PM -0800, David Kerr wrote:
- > I like the idea of load balancing, but how does that work, exactly, since Slony 
- > is asynchronous? 
- 
- You handle read-only and read-write queries differently.  Read-only
- queries get a consistent but not necessarily current view of the
- data.  So if your pattern is "update database, read results" with web
- pages, it just won't work -- you need the latest version of the data.
- For environments where imperfect currency is ok (think most web pages,
- for instance), it'll work.  But be careful: I never got pgpool to
- work well for me.

ok thanks. that's how i thought it would be. that may still work for one 
section of the app, but not the part i'm working on now.

- > Second for an HA solution, my real concern, if the load balancing isn't viable
- > (so to speak) can you configure PGPool to point to one node and then fail over
- > to another node (automatically) ? I understand that's a PGPool specific question
- > but since it seems like a common config with Slony I thought i'd chance it 
- > and ask here.
- 
- The question here is how much data loss you're willing to take.
- Alternatively, how much read-write downtime can you stand?
The app is 90% writing, so that'd be a problem.

- If you can stand to lose some transactions, then you can do full
- automatic failover.  But careful!  That data is lost more or less
- forever, so you need to be prepared for that.

I just can't justify losing committed transactions w/o large explosions
being involved so I don't think that would be good for me. :)

That's for the input that's exactly what I was looking for!

Dave