Parallel query execution

I mentioned last year that I wanted to start working on parallelism:
https://wiki.postgresql.org/wiki/Parallel_Query_Execution

Years ago I added thread-safety to libpq.  Recently I added two parallel
execution paths to pg_upgrade.  The first parallel path allows execution
of external binaries pg_dump and psql (to restore).  The second parallel
path does copy/link by calling fork/thread-safe C functions.  I was able
to do each in 2-3 days.

I believe it is time to start adding parallel execution to the backend. 
We already have some parallelism in the backend:
effective_io_concurrency and helper processes.  I think it is time we
start to consider additional options.

Parallelism isn't going to help all queries, in fact it might be just a
small subset, but it will be the larger queries.  The pg_upgrade
parallelism only helps clusters with multiple databases or tablespaces,
but the improvements are significant.

I have summarized my ideas by updating our Parallel Query Execution wiki
page: 
https://wiki.postgresql.org/wiki/Parallel_Query_Execution

Please consider updating the page yourself or posting your ideas to this
thread.  Thanks.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +