Re: Add cassert-only checks against unlocked use of relations

Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2013-11-05 16:25:53 -0500, Tom Lane wrote:
>> If we're sufficiently worried by this type of bug, ISTM we'd be better off
>> just disallowing heap_open(NoLock). At the time we invented that, every
>> lock request went to shared memory; but now that we have the local lock
>> table, re-locking just requires a local hash lookup followed by
>> incrementing a local counter. That's probably pretty cheap --- certainly
>> a lot cheaper than what you've got here.

> Hm. That only works though if we're using the same lockmode as before -
> often enough the *_open(NoLock) checks would use a weaker locklevel than
> the previous lock. So I think the cost of doing so would probably be
> noticeable.

If you're not using the same lockmode as before, it's probably a bug anyway.
As I said already, the entire NoLock coding technique is dependent on
having a very clear idea of which previous lock-taking you're riding
on the coattails of. Why wouldn't you duplicate that lock level,
if we say you can't use NoLock anymore?

regards, tom lane