Thread: Re: [COMMITTERS] pgsql: Temporarily (I hope) disable flattening of IN/EXISTS sublinks

Bruce Momjian <bruce@momjian.us> writes:
> Tom, you mentioned this should be a TODO item.  Do we put it on our main
> TODO, and if so, in what section?

Optimizer/executor I guess.  It's a pretty vague TODO though.  We need
some way to consider alternative join orders for joins that do not
semantically commute.  When I wrote that CVS log entry I was thinking
in terms of fixing the executor so that the joins actually could
commute, which would involve some way of separating the
force-vars-to-null behavior of an outer join from the actual execution
of the join.  I don't know how practical that really is though (and
also I've got a feeling it likely would fall foul of some patent or
other).  Or maybe it could be solved entirely in the planner, but I
don't have an idea of what the planner's internal representation would
have to look like to do that.
        regards, tom lane

Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Tom, you mentioned this should be a TODO item.  Do we put it on our main
> > TODO, and if so, in what section?
> 
> Optimizer/executor I guess.  It's a pretty vague TODO though.  We need
> some way to consider alternative join orders for joins that do not
> semantically commute.  When I wrote that CVS log entry I was thinking
> in terms of fixing the executor so that the joins actually could
> commute, which would involve some way of separating the
> force-vars-to-null behavior of an outer join from the actual execution
> of the join.  I don't know how practical that really is though (and
> also I've got a feeling it likely would fall foul of some patent or
> other).  Or maybe it could be solved entirely in the planner, but I
> don't have an idea of what the planner's internal representation would
> have to look like to do that.

Yea, this is beyond the detail we normally put in the TODO list.  If we
want to add this I am afraid we will need to document other optimizer
items as well.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +

Bruce Momjian wrote:

> Yea, this is beyond the detail we normally put in the TODO list.  If we
> want to add this I am afraid we will need to document other optimizer
> items as well.

FWIW you could just add all that text to a subpage of Todo, and point to
it from the regular TODO item.  For example the new page could be
Todo/FlattenInExistsSublinks (so it would be a page just for this
particular item).

Or, if you're feeling adventurous, you could name the new page
Todo/OptimizerAndPlanner and move all the items to it, with the same
formatting as the main Todo, and with whatever excruciating detail you
want.  Of course, there would still be a pointer to it from the main
Todo.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support