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

On Tue, Dec 8, 2020 at 10:41 AM Kyotaro Horiguchi
<horikyota(dot)ntt(at)gmail(dot)com> wrote:
>
> At Tue, 8 Dec 2020 08:08:25 +0530, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote in
> > On Tue, Dec 8, 2020 at 7:24 AM Kyotaro Horiguchi
> > <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> > > We drop
> > > buffers for the old relfilenode on truncation anyway.
> > >
> > > What I did is:
> > >
> > > a: Create a physical replication pair.
> > > b: On the master, create a table. (without explicitly starting a tx)
> > > c: On the master, insert a tuple into the table.
> > > d: On the master truncate the table.
> > >
> > > On the standby, smgrnblocks is called for the old relfilenode of the
> > > table at c, then the same function is called for the same relfilenode
> > > at d and the function takes the cached path.
> > >
> >
> > This is on the lines I have tried for recovery. So, it seems we are in
> > agreement that we can use the 'cached' flag in
> > DropRelFileNodesAllBuffers and it will take the optimized path in many
> > such cases, right?
>
>
> Mmm. There seems to be a misunderstanding.. What I opposed to is
> referring only to InRecovery and ignoring the value of "cached".
>

Okay, I think it was Kirk-San who proposed to use InRecovery and
ignoring the value of "cached" based on the theory that even if Insert
(or other DMLs) are done before Truncate, it won't use an optimized
path and I don't agree with the same. So, I did a small test to check
the same and found that it should use the optimized path and the same
is true for the experiment done by you. I am not sure why Kirk-San is
seeing something different?

> The remaining issue is we don't get to the optimized path when a
> standby makes the first call to smgrnblocks() when truncating a
> relation. Still we can get to the optimized path as far as any
> update(+insert) or select is performed earlier on the relation so I
> think it doesn't matter so match.
>

+1.

With Regards,
Amit Kapila.