Re: parallel joins, and better parallel explain
| От | Simon Riggs |
|---|---|
| Тема | Re: parallel joins, and better parallel explain |
| Дата | |
| Msg-id | CANP8+jLPb+Cd21qe3UL0=JrxAyb7MA18qgbtv7DEx5-uLy-jLw@mail.gmail.com обсуждение исходный текст |
| Ответ на | parallel joins, and better parallel explain (Robert Haas <robertmhaas@gmail.com>) |
| Ответы |
Re: parallel joins, and better parallel explain
|
| Список | pgsql-hackers |
On 26 November 2015 at 03:41, Robert Haas <robertmhaas@gmail.com> wrote:
--
Attached find a patch that does (mostly) two things. First, it allows
the optimizer to generate plans where a Nested Loop or Hash Join
appears below a Gather node. This is a big improvement on what we
have today, where only a sequential scan can be parallelized; with
this patch, entire join problems can be parallelized, as long as they
don't need a Merge Join (see below for more on this).
Sounds like good progress.
This gives us multiple copies of the hash table, which means we must either use N * work_mem, or we must limit the hash table to work_mem / N per partial plan.
How can the partial paths share a hash table?
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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