Re: Reviewing freeze map code

Hi Robert, Amit,

thanks for working on this.

On 2016-06-09 12:11:15 -0400, Robert Haas wrote:
> 4. The tests as written were not safe under concurrency; they could
> return spurious results if the page changed between the time you
> checked the visibility map and the time you actually examined the
> tuples. I think people will try running these functions on live
> systems, so I changed the code to recheck the VM bits after locking
> the page. Unfortunately, there's either still a concurrency-related
> problem here or there's a bug in the all-frozen code itself because I
> once managed to get pg_check_frozen('pgbench_accounts') to return a
> TID while pgbench was running concurrently. That's a bit alarming,
> but since I can't reproduce it I don't really have a clue how to track
> down the problem.

Ugh, that's a bit concerning.

> If there are not objections, I will go ahead and commit this tomorrow,
> because even if there is a bug (see point #4 above) I think it's
> better to have this in the tree than not. However, code review and/or
> testing with these new functions seems like it would be an extremely
> good idea.

I'll try to spend some time on that today (code review & testing).

Andres