Re: SKIP LOCKED DATA (work in progress)

On 07/31/2014 12:29 AM, Thomas Munro wrote:
> On 29 July 2014 02:35, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
>> David Rowley wrote:
>>
>>> I've also been looking at the isolation tests and I see that you've added a
>>> series of tests for NOWAIT. I was wondering why you did that as that's
>>> really existing code, probably if you thought the tests were a bit thin
>>> around NOWAIT then maybe that should be a separate patch?
>>
>> The isolation tester is new so we don't have nearly enough tests for it.
>> Adding more meaningful tests is good even if they're unrelated to the
>> patch at hand.
>
> Here are my isolation tests for NOWAIT as a separate patch,
> independent of SKIP LOCKED.  They cover the tuple lock, regular row
> lock and multixact row lock cases.

Thanks, committed.

> I guess this might be called white
> box testing, since it usese knowledge of how to construct schedules
> that hit the three interesting code paths that trigger the error, even
> though you can't see from the output why the error was raised in each
> case without extra instrumentation (though it did cross my mind that
> it could be interesting at the very least for testing if the error
> message were different in each case).

Yeah, seems reasonable. This kind of tests might become obsolete in the 
future if the internals change a lot, so that e.g. we don't use 
multixids anymore. But even if that happens, there's little harm in 
keeping the tests, and meanwhile it's good to have coverage of these cases.

- Heikki