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update, truncate and vacuum

From: Scott Feldstein <scott(dot)feldstein(at)hyperic(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: update, truncate and vacuum
Date: 2007-07-26 22:36:50
Message-ID: B195EEA2-7B5D-444F-8F48-46BB88FCFFA8@hyperic.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,
I have a couple questions about how update, truncate and vacuum would  
work together.

1) If I update a table foo (id int, value numeric (20, 6))
with
update foo set value = 100 where id = 1

Would a vacuum be necessary after this type of operation since the  
updated value is a numeric? (as opposed to a sql type where its size  
could potentially change i.e varchar)

2) After several updates/deletes to a table, if I truncate it, would  
it be necessary to run vacuum in order to reclaim the space?

thanks,
Scott

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