On Thu, Sep 15, 2016 at 9:59 AM, Tom Lane <t...@sss.pgh.pa.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. It seemed best to insist that the relation had a reasonable number of blocks so that we could hope for a reasonably even distribution of work among a pool of workers. I'm not altogether sure that's the right way of thinking about this problem but I'm not sure it's wrong, either; anyway, it's as far as my thought process had progressed at the time I wrote the code. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
