Re: Deleting bytea, autovacuum, and 8.2/8.4 differences

On Mon, 15 Mar 2010, Tom Lane wrote:
> For an example like this one, you have to keep in mind that the
> toast-table rows for the large bytea value have to be marked deleted,
> too.  Also, since I/O happens in units of pages, the I/O volume to
> delete a tuple is just as much as the I/O to create it.  (The WAL
> entry for deletion might be smaller, but that's all.)  So it is entirely
> unsurprising that "DELETE FROM foo" is about as expensive as filling the
> table initially.
>
> If deleting a whole table is significant for you performance-wise,
> you might look into using TRUNCATE instead.

What are the implications of using TRUNCATE on a table that has TOASTed
data? Is TOAST all stored in one single table, or is it split up by owner
table/column name? Might you still end up with a normal delete operation
on the TOAST table when performing a TRUNCATE on the owner table?

Matthew

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