Slow insert/delete

I am in the process of converting an old system to a
new system where I have chosen to use postgres in
stead of a home grow system based on b-trees.

The system receives 2650 message a total of 10Mbytes
of data per 15 minutes this information have to be
store in 4 tables in the database. Some of the
messages are updates to existing data and the result
is:
1038 records in table 1 size per record 282 bytes
2074 records in table 2 size per record 36 bytes
21488 records in table 3 size per record 60 bytes
25676 records in table 4 size per record 42 bytes.

Without indexes this should be something like
2,7Mbytes/15min.

The disk speed is as follows taken from hdparm -Tt
/dev/hda:
Timing buffer-cache reads: 128 MB in 0.89 seconds
=143.82 MB/sec
Timing buffered disk reads: 64 MB in 1.45 seconds =
44.14 MB/sec

My problem is that the postmaster process is using
between 70-90% of the CPU time. (seen using top) and
the total wall time with nothing else running.

It takes 6 minutes to ingest the data with an empty
database and 25 minutes (wall time) if all the data is
already in the database.
The processing is done as follows:
1. Start transaction

2. check if message is in table 1 and if so delete
records from table 1(1 row),2(2 rows),3(30 rows),4(50
rows).

3. split the message and insert the date in table 1(1
row),2(2 rows),3(30 rows),4(50 rows)

4. end transaction

I need some suggestions so that I can ingest the data
faster. with the same computer and disks. We are
running redhat 7.2 on the server and I am using the c
interface to write the data to the server.

Thanks for any help,
Thor.

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