Re: Reviewing freeze map code

On 2016-06-10 11:58:26 +0530, Amit Kapila wrote:
> I have tried in multiple ways by running pgbench with read-write tests, but
> could not see any such behaviour.

It took over an hour of pgbench on a fast laptop till I saw it.

> I have tried by even crashing and
> restarting the server and then again running pgbench. Do you see these
> records on master or slave?

Master, but with an existing standby. So it could be related to
hot_standby_feedback or such.

> While looking at code in this area, I observed that during replay of
> records (heap_xlog_delete), we first clear the vm, then update the page.
> So we don't have Buffer lock while updating the vm where as in the patch
> (collect_corrupt_items()), we are relying on the fact that for clearing vm
> bit one needs to acquire buffer lock. Can that cause a problem?

Unsetting a vm bit is always safe, right? The invariant is that the VM
may never falsely say all_visible/frozen, but it's perfectly ok for a
page to be all_visible/frozen, without the VM bit being present.

Andres