Re: How many Cluster database on a single server - Mailing list pgsql-performance

Hi Craig,
thanks for your reply. I think I need to add some details on my
question, like why we would need more than one Cluster Database. We are
thinking to use the Streaming Replica feature to keep in sync a number
of little DB servers around the net. The replica should happen on one or
more centralized servers. I didn't tested the replica personally bus as
I can see, it syncs the whole Cluster DB. So, on the centralized
server(s), we will have perfect copies of the Cluster Databases.
We sure need to test this configuration but first of all I was wondering
if there are known drawbacks.
Thanks again.


On 10/19/2011 03:54 PM, Craig James wrote:
> On 10/19/11 2:46 AM, d.davolio@mastertraining.it wrote:
>> Hi everybody,
>> I googled a bit around and also checked the mailing lists but I still
>> can't make an idea. We plan to use postgres 9 and the Cluster
>> Database Replica.
>> My colleagues are asking how many Cluster Databases (initdb) can I
>> create and run on a single server. I mean, supposed my server has the
>> resources, can I create 100 or even 200 Cluster Databases? Everyone
>> with the right configuration and in respect of the requisites?
>> Or the postgres architecture doesn't provide similar numbers?
>> We are thinking to use the replica from near 200 databases around the
>> internet on a single db server.
> You don't need to do initdb on each one. Postgres can create many
> databases on a single server and manage them without difficulty.
>
> We currently operate about 300 databases on a single server.  Most are
> small, and one is an aggregate of all the small ones.  I believe there
> are sites that have >1000 separate databases on one server.
>
> Postgres has a slightly different concept of a "database" than Oracle
> or MySQL, which is why your question about initdb is slightly off.
> You can indeed create several separate instances of Postgres (separate
> initdb for each), but the only reason you ever need to do that is if
> you're running different versions of Postgres (like 8.4 and 9.0)
> simultaneously.
>
> Postgres runs into problems when the total number of objects (tables,
> views, sequences, ...) across all databases gets very large, where
> "very large" is ill defined but is somewhere between a few hundred
> thousand and a million.  We once had a rogue process that created 5
> million tables, and we had to completely abandon the installation
> because of some sort of N^2 phenomenon that made it impossible to even
> use pg_dump to save and restore the system.  So the advice is, "don't
> do dumb stuff like that" and you should be able to manage many databases.
>
> Craig
>
>