Mass updates on a large table

Good afternoon,

I am attempting an update on two new date field columns on a 17 million row
table. Every row gets updated.

The update statement is a simple one:

UPDATE EMAILRCPTS SET ID = ID

And the update of the new date fields themselves occurs as the result of a
before trigger.

The update took 3 days, 10 hours to complete on the testing box. I have
already adjusted the CHECKPOINT_SEGMENTS parameter up by 3X

To minimize the impact of checkpoints. The SHARED_BUFFERS parameter has
been bumped up to 140000 on a 20meg RAM box.

There are about 9 indexes on this table although none of them reference the
date fields so since there are no inserts I don't think they would have an
impact on the update (I've been wrong before though)

Would an update statement referencing the date fields work faster than a
trigger? Do you have any other suggestions to speed this up?

We simply cannot afford this table to be down for 3+ days during a
production update. The production box is a 32meg RAM box.

We are at Postgres 7.4.5.

Thanks for your time and brainpower

Mark Steben

Senior Database Administrator
@utoRevenueT
A Dominion Enterprises Company
480 Pleasant Street
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