Q: Reclaiming deleted space in data files

If I insert a large amount of data into a Postgres
table, so that the data file (or files) grow by a
large amount (something in the gigabyte range), and I
subsequently delete the table containing this data (or
delete the data from the table), can I reclaim the
space without major hassle?

I'm guessing I can with the VACUUM command. Are there
any other mechanisms for this? How "long" would it
take, i.e. if I had deleted a gigabyte of data, is
this vacuum process going to be something which
happens quickly, i.e. a matter of minutes, or is it
the kind of thing which will thrash for days and block
the DB? (I appreciate the precise timing will depend
on the size and structure of the DB, hardware etc.).

Please understand I'm not intending to do this kind of
thing often, but I have gotten into this problem with
my current DB setup and it's given me the impetus to
look for possible alternatives.


Thx

Lawrence Smith



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