Re: Vacuum: allow usage of more than 1GB of work mem

On Wed, Sep 7, 2016 at 1:45 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 6 September 2016 at 19:59, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> The idea of looking to the stats to *guess* about how many tuples are
>> removable doesn't seem bad at all. But imagining that that's going to be
>> exact is folly of the first magnitude.
>
> Yes. Bear in mind I had already referred to allowing +10% to be safe,
> so I think we agree that a reasonably accurate, yet imprecise
> calculation is possible in most cases.

That would all be well and good if it weren't trivial to do what
Robert suggested. This is just a large unsorted list that we need to
iterate throught. Just allocate chunks of a few megabytes and when
it's full allocate a new chunk and keep going. There's no need to get
tricky with estimates and resizing and whatever.

--
greg