Re: select_parallel test fails with nonstandard block size

On Thu, Sep 15, 2016 at 10:44 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> 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.

I don't particularly care about that. Changing it to 8MB always would
be fine with me.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company