On Fri, Nov 30, 2007 at 10:30:47PM +0100, Pascal Cohen wrote:
I am facing a probably very common problem. I made a search in the
recent archives and could find many posts related to my issue. But I did
not get exactly "the answer" to my question.
No, and I doubt you will.
I don't why I had such a feeling ;)
Thanks for your answer. It was an open question and your answer
concerning Log-Shipping/Slony is very helpful.
But I don't know how to chose a solution. I don't have much experience
and can't see precisely the advantages and the drawbacks of each solution.
That's because, quite frankly, it's hard to answer that question in general.
You have to answer it under your circumstances. Since you're the one who
knows those, you'll have to do the answering, I'm afraid. This probably
means "do some tests".
That is what I am currently doing.
My purpose is to study (we are absolutely not in a hurry so I have time
to evaluate all the cases) how to handle:
High-availability and scalability in our environment where there are
many reads and few writes.
* For High-availability, I mainly studied PgPool and Log-shipping (and
in fact forgot Slony).
Until now I feel more comfortable with Log-shipping because it seems
safer (I am not sure I can't get some problems with sequences and
current_timestamp with PgPool - it is even mentioned in the doc).
* For Scalability, I had a look to sharding, and tried to look at
replication/load-balancing.
For load-balancing, I really appreciated PgPool, but again the statement
replication does not make me really comfortable so I studied two ways:
Synchronous replication and asynchronous replication.
I think that synchronous synchronization is a nice to have feature but
absolutely not mandatory. So if I am concerned by scalability, I think
we can avoid overload caused by synchronous solution.
For now I think using PgPool as a load-balancer while Slony handles
Master-Slave replication seems a good solution.
But I will anyway have a look to CyberCluster.
And why should I chose Slony instead of Log-shipping to update the slaves ?
This is a good example (and the only thing in your list I feel comfortable
talking about): if you think that you might find it handy to be able to
query the replicas, use Slony, because you can't do it with log shipping
(yet).
Do you mean that Log-shipping is well for a Standby server not handling
request while Slony is good with "select" load balancing ?
Why and what limits Log-shipping for that case ?
Thanks for the answer!
Pascal
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