Re: parallel joins, and better parallel explain

On 26 November 2015 at 03:41, Robert Haas <robertmhaas(at)gmail(dot)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?

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