Re: Performance degradation of REFRESH MATERIALIZED VIEW

Hi,

On 2021-04-26 23:59:17 +0200, Tomas Vondra wrote:
> On 4/26/21 9:27 PM, Andres Freund wrote:
> > On 2021-04-26 15:31:02 +0200, Tomas Vondra wrote:
> > > I'm not sure what to do about this :-( I don't have any ideas about how to
> > > eliminate this overhead, so the only option I see is reverting the changes
> > > in heap_insert. Unfortunately, that'd mean inserts into TOAST tables won't
> > > be frozen ...
> > 
> > ISTM that the fundamental issue here is not that we acquire pins that we
> > shouldn't, but that we do so at a much higher frequency than needed.
> > 
> > It's probably too invasive for 14, but I think it might be worth exploring
> > passing down a BulkInsertState in nodeModifyTable.c's table_tuple_insert() iff
> > the input will be more than one row.
> > 
> > And then add the vm buffer of the target page to BulkInsertState, so that
> > hio.c can avoid re-pinning the buffer.
> > 
> 
> Yeah. The question still is what to do about 14, though. Shall we leave the
> code as it is now, or should we change it somehow? It seem a bit unfortunate
> that a COPY FREEZE optimization should negatively influence other (more)
> common use cases, so I guess we can't just keep the current code ...

I'd suggest prototyping the use of BulkInsertState in nodeModifyTable.c
and see whether that fixes the regression. If it does, then we can
analyze whether that's possibly the best way forward. Or whether we
revert, live with the regression or find yet another path.

Greetings,

Andres Freund