Re: hash_xlog_split_allocate_page: failed to acquire cleanup lock

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I had that thought too, but I don't *think* it's the case. This
> function acquires a lock on the oldest bucket page, then on the new
> bucket page. We could deadlock if someone who holds a pin on the new
> bucket page tries to take a content lock on the old bucket page. But
> who would do that? The new bucket page isn't yet linked from the
> metapage at this point, so no scan should do that. There can be no
> concurrent writers during replay. I think that if someone else has the
> new page pinned they probably should not be taking content locks on
> other buffers at the same time.

Agreed, the core code shouldn't do that, but somebody doing random stuff
with pageinspect functions could probably make a query do this.
See [1]; unless we're going to reject that bug with "don't do that",
I'm not too comfortable with this line of reasoning.

regards, tom lane

[1] https://www.postgresql.org/message-id/flat/17568-ef121b956ec1559c%40postgresql.org