On Tue, Mar 21, 2017 at 01:04:14PM -0400, Robert Haas wrote:
> > I know we have talked about it, but not recently, and if everyone else
> > is fine with it, I am too, but I have to ask these questions.
>
> I think that's a good question. I previously expressed similar
> concerns. On the one hand, it's hard to ignore the fact that, in the
> cases where this wins, it already buys us a lot of performance
> improvement. On the other hand, as you say (and as I said), it eats
> up a lot of bits, and that limits what we can do in the future. On
> the one hand, there is a saying that a bird in the hand is worth two
> in the bush. On the other hand, there is also a saying that one
> should not paint oneself into the corner.
>
> I'm not sure we've had any really substantive discussion of these
> issues. Pavan's response to my previous comments was basically "well,
> I think it's worth it", which is entirely reasonable, because he
> presumably wouldn't have written the patch that way if he thought it
> sucked. But it might not be the only opinion.
Early in the discussion we talked about allowing multiple changes per
WARM chain if they all changed the same index and were in the same
direction so there were no duplicates, but it was complicated. There
was also discussion about checking the index during INSERT/UPDATE to see
if there was a duplicate. However, those ideas never led to further
discussion.
I know the current patch yields good results, but only on a narrow test
case, so I am not ready to just stop asking questions based the opinion
of the author or test results alone.
If someone came to me and said, "We have thought about allowing more
than one index change per WARM chain, and if we can ever do it, it will
probably be done this way, and we have the bits for it," I would be more
comfortable.
One interesting side-issue is that indirect indexes have a similar
problem with duplicate index entries, and there is no plan on how to fix
that either. I guess I just don't feel we have explored the
duplicate-index-entry problem enough for me to be comfortable.
-- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB
http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
