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List:       postgresql-general
Subject:    Re: [GENERAL] truncate/create slowness
From:       Tom Lane <tgl () sss ! pgh ! pa ! us>
Date:       2005-03-31 23:33:32
Message-ID: 1551.1112312012 () sss ! pgh ! pa ! us
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"Julian Scarfe" <julian@avbrief.com> writes:
> Do you have any rules of thumb for deciding when a pg_dumpall/restore is 
> likely to be faster than a vacuum full?  Or perhaps more straightforwardly, 
> how would you expect the time required for a vacuum full to scale with pages 
> used and rows in the table?

There is a factor that's proportional to the number of tuples deleted,
and a bigger factor that's proportional to the number of tuples moved
while trying to compact the table.  If you've got a seriously bloated
table then it's fairly likely that *all* the surviving tuples will get
moved because none of them are near the start of the table already :-(

Having said that, though, a vacuum full and reindex on pg_class and
pg_attribute will certainly solve Steve's problem faster than a dump
and reload, simply because there's not much stuff in those catalogs
compared to any reasonably-sized user tables.

			regards, tom lane

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