Pgsql vs Interbase: Transaction benchmark

Hi to all!
I'm doing some benchmarks to test Interbase vs PostgreSQL. The
test are done with the respective PHP client. The two servers are installed
on the same machine with RedHat 7.0.
Pgsql has been started with these configuration options:
- sort_mem = 512
- fsync = false
- shared_buffers = 1024
- commit_delay = 0
- commit_siblings = 1
Interbase is installed with the default options.

The test consists of these operations:
- START TRANSACTION
- for i = 1 to 100
- SELECT
- UPDATE (on the same row of the select)
- end for
- END TRANSACTION

Each transaction is then repeated 100 times by 10 different clients. The
transaction type is READ_COMMITTED in both servers.
All the operations are perfomed in the same table with 1.000.000 of records
and the searches (those specified by the WHERE clause of SELECT and UPDATE)
are done only on the primary key of the table itself.
I calculated the mean duration of a transaction and the machine load
(obtained using the w command). The results are:

INTERBASE (6.0.1)
Average Machine Load: 5.00
Duration of a transaction: 23 s

POSTGRESQL (7.1.1)
Average Machine Load: 10.00
Duration of a transaction: 40 s

I've also done a test without client concurrent select/updates (with only
one client...) and the results are:
INTERBASE
Average Machine Load: 0.40
Duration of a transaction: 7.5 s

POSTGRESQL
Average Machine Load: 1.10
Duration of a transaction: 6.4 s

Is there anything I can do to speed-up PostgreSQL? Is there anything wrong
in my configuration parameters?

The machine has 128Mb of memory and the processor is a PII 350Mhz.

Thank you in advance for your replyies and comments,

Denis
-------------------
denis(at)edistar(dot)com