Re: Allowing NOT IN to use ANTI joins

On 24 June 2014 23:44, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
>> Having said that, any join plan that relies upon a constraint will
>> still be valid even if we drop a constraint while the plan executes
>> because any new writes will not be visible to the executing join plan.
>
> mumble ... EvalPlanQual ?

As long as we are relaxing a constraint, we are OK if an earlier
snapshot thinks its dealing with a tighter constraint whereas the new
reality is a relaxed constraint.

The worst that could happen is we hit an ERROR from a constraint that
was in force at the start of the query, so for consistency we really
should be enforcing the same constraint throughout the lifetime of the
query.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services