Craig Ringer wrote:
Robert Powell wrote:
To whom it may concern,
I'm looking for a file server that will give me a high level of
redundancy and high performance for a postgres database.
For strong redundancy and availability you may need a secondary server
and some sort of replication setup (be it a WAL-following warm spare,
slony-I, or whatever). It depends on what you mean by "high".
As for performance - I'm still learning on this myself, so treat the
following as being of questionable accuracy.
As far as I know the general rule for databases is "if in doubt, add
more fast disks". A fast CPU (or depending on type of workload several
almost-as-fast CPUs) will be nice, but if your database is big enough
not to fit mostly in RAM you'll mostly be limited by disk I/O. To
increase disk I/O performance, in general you want more disks. Faster
disks will help, but probably not as much as just having more of them.
More RAM is of course also nice, but might make a huge difference for
some workloads and database types and relatively little for others. If
doubling your RAM lets the server cache most of the database in RAM
it'll probably speed things up a lot. If doubling the RAM is the
difference between 2% and 4% of the DB in RAM ... it might not make
such a difference (unless, of course, your queries mostly operate on a
subset of your data that's fairly similar to your RAM size, you do
lots of big joins, etc).
Various RAID types also have implications for disk I/O. For example,
RAID-5 tends to have miserable write performance.
In the end, though, it depends a huge amount on your workload. Will
you have huge numbers of simpler concurrent transactions, or
relatively few heavy and complex ones? Will the database be
read-mostly, or will it be written to very heavily? Vaguely how large
is your expected dataset? Is all the data likely to be accessed with
equal frequency or are most queries likely to concentrate on a small
subset of the data? And so on...
--
Craig Ringer
The key issue on RAM is not whether the database will fit into RAM (for
all but the most trivial applications, it will not)
It is whether the key INDICES will fit into RAM. If they will, then you
get a HUGE win in performance.
If not, then it is all about disk I/O performance and the better you can
spread that load across multiple spindles and get the data into the CPU
at a very high rate of speed, the faster the system will perform.
In terms of redundancy you have to know your workload before designing a
strategy. For a database that is almost all queries (few
inserts/updates) the job is considerably simpler than a database that
sees very frequent inserts and/or updates.
Karl Denninger (karl@xxxxxxxxxxxxx)
http://www.denninger.net
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