Re: [Patch] Optimize dropping of relation buffers using dlist

At Tue, 08 Dec 2020 09:45:53 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> At Mon, 7 Dec 2020 17:18:31 +0530, Amit Kapila <amit.kapila16@gmail.com> wrote in 
> > Hmm, how is it possible if Insert is done before Truncate? The insert
> > should happen in old RelFileNode only. I have verified by adding a
> > break-in (while (1), so that it stops there) heap_xlog_insert and
> > DropRelFileNodesAllBuffers(), and both get the same (old) RelFileNode.
> > How have you verified what you are saying?
> 
> You might be thinking of in-transaction sequence of
> Inert-truncate. What *I* mention before is truncation of a relation
> that smgrnblocks() has already been called for.  The most common way
> to make it happen was INSERTs *before* the truncating transaction
> starts. It may be a SELECT on a hot-standby.  Sorry for the confusing
> expression.

And ,to make sure, it is a bit off from the point of the discussion as
I noted.  I just meant that the proposition that "smgrnblokcs() always
returns false for "cached" when it is called in
DropRelFileNodesAllBuffers()" doesn't always holds.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center