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

On 3 September 2016 at 04:25, Claudio Freire <klaussfreire@gmail.com> wrote:
> The attached patch allows setting maintainance_work_mem or
> autovacuum_work_mem higher than 1GB (and be effective), by turning the
> allocation of the dead_tuples into a huge allocation.
>
> This results in fewer index scans for heavily bloated tables, and
> could be a lifesaver in many situations (in particular, the situation
> I'm living right now in production, where we don't have enough room
> for a vacuum full, and have just deleted 75% of a table to make room
> but have to rely on regular lazy vacuum to free the space).

This part looks fine. I'm inclined to commit the attached patch soon.

> The patch also makes vacuum free the dead_tuples before starting
> truncation. It didn't seem necessary to hold onto it beyond that
> point, and it might help give the OS more cache, especially if work
> mem is configured very high to avoid multiple index scans.

How long does that part ever take? Is there any substantial gain from this?

Lets discuss that as a potential second patch.

> Tested with pgbench scale 4000 after deleting the whole
> pgbench_accounts table, seemed to work fine.

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