Re: Hardware impact on performances

Camille Chafer wrote:
> Hi,
>
> I'm using PostgreSQL 8 for a mmorpg.
> The part of each operation is : select: 50%, update: 40%, insert: 10%.
> I have no more than 4-5 concurrent connections to the database, but each
> of them does A LOT of queries (several per second).
> The database size is about 1GB, but it'll probably be around 2GB in a
> fews months.
> The OS will be FreeBSD (version production 5.3 probably, or 4.10)
>
> At this time, i'm looking for a new server. Before to buy it, I grab
> some informations..
> So, my question is : what would be the best hardware for this type of
> needs ?
> Of course, I'm not asking for a trademark and/or for prices, but for hints.
>
> - What is the most important part of the system : CPU ? RAM ? Disks ?

Usually Disks/RAM. Since you've got a lot of updates/inserts,
battery-backed write-cache on your raid controller would be good.

> - Is a server with 2 or more CPUs much better than a server with a
> single one, for a pgsql database ?

With 2+ connections, each can be serviced by one CPU. Of course, if your
disk I/O is saturated then it won't help.

> - How much RAM do I need ? The size of the data ? Twice the size ?

Ideally, enough to hold your "working set". That is, enough cache to
store all pages/indexes you regularly access.

> - I heard Raid1+0 is better than Raid 5. Is it right ? What would be the
> best configuration, regarding performances and security ?

It can depend - check the list archives for a lot of discussion on this.
More disks is always better.

> - Does the CPU type (i386, PowerPC, ....) matters ?

Dual-Xeons have given problems. A lot of people seem to think
Opteron-based systems provide good value.

> - A lot of queries probably generate a lot of network output. Does the
> network controller matters ?

Well, obviously the more time spent handling network I/O, the less time
you spend running queries. I'd think it would have to be a *lot* of
activity to make a serious difference.

> - And finally, last question : is it possible to run a single postgresql
> database on several servers ? (hardware clustering)

Not easily, and it probably wouldn't provide any performance benefit.
Plenty of replication options though.

> Thanks in advance for your answers, and sorry for my crap english (i'm
> french).

Your English is perfect.
--
Richard Huxton
Archonet Ltd