Greg Stark <stark@mit.edu> writes:
> On Sat, Nov 1, 2014 at 9:09 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> 2. Syscache lookups had better work in parallel workers, or they'll be
>> all but useless.
> I've been using parallel sorts and index builds in my mental model of
> how this will be used. I note that sorts go out of their way to look
> up all the syscache entries in advance precisely so that tuplesort
> doesn't start doing catalog lookups in the middle of the sort.
Well, they try to avoid doing the lookups more than once, but that does
not by any means imply that no lookups happen after the sort starts.
In particular, if you're sorting a container type (array, record)
there will be lookups during the first call of the sort type's comparison
function. Enums could cause catalog lookups much later than the first
call, too.
I'm with Robert: if you cannot do catalog lookups in a worker process,
the feature will be so crippled as to be essentially useless.
regards, tom lane
