Re: VACUUM FULL vs dropped columns

On Sun, Mar 11, 2018 at 9:49 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> writes:
>> Why does VACUUM FULL cause the size of this table with a single
>> dropped column (1 out of 1000) cause the table size to double?
>
> VACUUM FULL will rewrite the tuples with a null bitmap where they
> had none before (cf reform_and_rewrite_tuple). That's only a rather
> marginal increase in the tuple size, but in this particular example,
> it pushes the tuples from just under half a page to just over, so
> that you go from 2 tuples/page to 1.
>

Aha! Thanks for the explanation.

cheers

andrew

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Andrew Dunstan https://www.2ndQuadrant.com
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