On Thu, Nov 2, 2017 at 8:01 AM, Craig Ringer <cr...@2ndquadrant.com> wrote:
> That forces materialization, and I'm guessing part of Tomas's goal
> here is to prevent the need to materialize into a temp table /
> tuplestore / etc.

I get that, but if you're running a query like "SELECT * FROM
bigtable", you don't need parallel query in the first place, because a
single backend is quite capable of sending back the rows as fast as a
client can read them.  If you're running a query like "SELECT * FROM
bigtable WHERE <highly selective predicate>" then that's a good use
case for parallel query, but then materializing it isn't that bad
because the result set is a lot smaller than the original table.

I am not disputing the idea that there are *some* cases where parallel
query is useful and materialization is still undesirable, of course.

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

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