Re: Status of the table access method work

Hi,

On 2019-04-10 20:14:17 +0300, Alexander Korotkov wrote:
> Your explanation of existing limitations looks very good and
> convincing. But I think there is one you didn't mention. We require
> new table AMs to basically save old "contract" between heap and
> indexes. We have "all or nothing" choice during updates. So, storage
> can either insert to none of indexes or insert to all of them
> (HOT-like update).

I think that's a problem, and yea, I should have mentioned it. I'd
earlier thought about it and then forgot.

I however don't think we should design the interface for this before we
have at least one AM that's actually in decent-ish shape that needs
it. I seriously doubt we'll get the interface right enough.

Note: I'm *extremely* *extremely* doubtful that moving the full executor
invocations for expression indices etc into the tableam is a sane thing
to do. It's possible to convince me there's no alternative, but it'll be
really hard.

I suspect the right direction will be more going in a direction of
computing new index tuples for expression indexes before tableam gets
involved. If we do that right, we can also implement the stuff that
1c53c4dec3985512f7f2f53c9d76a5295cd0a2dd reverted in a proper way.

> I think any storage, which is going to address "write amplification"
> point raised by Uber, needs to break this "contract".

FWIW, I don't think it makes much point in using Uber as a justification
for anything here. Their analysis was so deeply flawed and motivated by
non-technical reasons that it should just be ignored.

Greetings,

Andres Freund