Re: Suspicious behaviour on applying XLOG_HEAP2_VISIBLE.

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Apr 14, 2016 at 12:11 PM, Andres Freund <andres@anarazel.de> wrote:
>> The easiest way to achieve that seems to be to just assign an xid if
>> that's the case; while it's not necessarily safe/efficient to do so at
>> the point the invalidation message was queued, I think it should be safe
>> to do so at commit time. Seems less invasive to backpatch than to either
>> support commit records without xids, or a separate record just
>> transporting invalidation messages.

> I agree that's better for back-patching.  I hope it won't suck
> performance-wise.  In master, we might think of inventing something
> new.

I'm a little worried about whether this will break assumptions that
vacuum doesn't have an XID.  I don't immediately see how it would,
but it seems a bit shaky.

I find it hard to believe that the act of assigning an XID would add
measurably to the cost of a vacuum, so Robert's performance concern
doesn't sound very exciting.  If this works, I think it's fine to
adopt as a permanent solution.
        regards, tom lane