Re: select_parallel test fails with nonstandard block size

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Sep 15, 2016 at 9:59 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Possibly we ought to change things so that the default value of
>> min_parallel_relation_size is a fixed number of bytes rather
>> than a fixed number of blocks. Not sure though.

> The reason why this was originally reckoned in blocks is because the
> data is divided between the workers on the basis of a block number.
> In the degenerate case where blocks < workers, the extra workers will
> get no blocks at all, and thus no rows at all.

Well, sure, but at any reasonable value of min_parallel_relation_size
that won't be a factor. The question here is whether we want the default
value to be platform-independent. I notice that both config.sgml and
postgresql.conf.sample claim that the default value is 8MB, which this
discussion reveals to be a lie. If you want to keep the default expressed
as "1024" and not "(8 * 1024 * 1024) / BLCKSZ", we need to change the
documentation.

regards, tom lane