Hi

I tried pgpool2 + slony-1 replication in master/slave and load_balance=false
and replicate_select = false mode. It works fine. The only big problem is
that i thought pgpool will send all my write queries to the master and all
my read queries to the slave. But i am not sure that it does this. Any help?



Andrew Sullivan-8 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.
> 
>> 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?
> 
> If you MUST have an up-to-date view of the data, but if the read-write
> node fails you can just live with reads, then you're golden.  Set up
> two pools.  Pool 1 is for read-write and read, and handles all the
> data under normal circumstances.  Pool 2 is a standby, and if the
> database on pool 1 is lost, it takes over.  Write transactions on this
> pool always fail, but it will allow you to do read-only for as long as
> you still have a good database system there.  The data is current as
> of the last applied snapshot (which need not be the last write action
> in the data origin, but it might be good enough).
> 
> 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.
> 
> A
> 
> -- 
> Andrew Sullivan
> ajs at crankycanuck.ca
> _______________________________________________
> Slony1-general mailing list
> Slony1-general at lists.slony.info
> http://lists.slony.info/mailman/listinfo/slony1-general
> 
> 

-- 
View this message in context: http://old.nabble.com/Slony-%2B-PGPool-for-HA-Failover-only-tp26400286p29032292.html
Sent from the Slony-I -- General mailing list archive at Nabble.com.