| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Greg Stark <stark(at)mit(dot)edu>, Marti Raudsepp <marti(at)juffo(dot)org>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Allowing NOT IN to use ANTI joins |
| Date: | 2014-06-24 22:48:44 |
| Message-ID: | CA+U5nMJGuzD-inHr-bR+ogueCQnbCX4BU-c8z73cK_HwF7AdCg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 24 June 2014 23:44, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)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
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