Re: WIP: generalized index constraints

Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Sat, 2009-09-19 at 18:00 -0400, Tom Lane wrote:
>> Well, you can't do it *exactly* the same way btree does, but what
>> I would envision is first insert the index tuple and then do a
>> dirty-snapshot search for conflicting tuples. The interlock against
>> conflicting concurrent inserts doesn't need all this new infrastructure
>> you propose; just wait to see if conflicting transactions commit, same
>> as we do now. And I do maintain that that sort of code has a high risk
>> of undetected bugs.

> How do you prevent deadlocks in the following case?

> T1: inserts into index
> T2: inserts into index
> T1: checks index for conflicts, finds T2
> T2: checks index for conflicts, finds T1

You get a deadlock failure, because both transactions will wait for each
other. So what? It's an error in any case, and you can get a reported
deadlock in constraint-enforcement scenarios today (conflicting FK
changes, for instance).

regards, tom lane