On Tue, Jan 10, 2017 at 6:42 AM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>> Does this work negate the other work to allow VACUUM to use >
>> 1GB memory?
>
> Partly yes. Because memory space for dead TIDs needs to be allocated
> in DSM before vacuum worker launches, parallel lazy vacuum cannot use
> such a variable amount of memory as that work does. But in
> non-parallel lazy vacuum, that work would be effective. We might be
> able to do similar thing using DSA but I'm not sure that is better.
I think it would work well with DSA as well.
Just instead of having a single segment list, you'd have one per worker.
Since workers work on disjoint tid sets, that shouldn't pose a problem.
The segment list can be joined together later rather efficiently
(simple logical joining of the segment pointer arrays) for the index
scan phases.