Postgres batch write very slow - what to do

Folks !

I have a batch application that writes approx. 4 million rows into a narrow
table. I am using JDBC addBatch/ExecuteBatch with auto commit turned off.
Batch size is 100. So far I am seeing Postgres take roughly five times the
time it takes to do this in the Oracle.

I have played with many parameters. Only one that seems to have any affect
is fsync - but thats only 10% or so.
Initially I got the warning that checkpoints were happening too often so I
increased the segments to 24. Warnings stopped, but no real improvement in
performance.

Is postgres really that slow ? What am I missing ?

Here are the changes to my postgressql.cong file.

shared_buffers = 768MB
work_mem = 256MB
maintenance_work_mem = 128MB
fsync = off

checkpoint_segments = 24
autovacuum = on

Thank you,

-Sanjay
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