Re: WIP: Rework access method interface

Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> writes:
> [ aminterface-13.patch ]

I've started to review this. There are a bunch of cosmetic things I don't
like, notably the include-file nesting you've chosen, but they're fixable.
One item that I think could use some discussion is where to put the new
amvalidate functions. I don't especially like your choice to drop them
into nbtree.c, gist.c, etc, for a couple of reasons:

1. These aren't really at the same semantic level as functions like
btinsert or btgettuple; they're not part of the implementation of an
index, and indeed are *users* of indexes (at least of the catalog
indexes).

2. This approach substantially bloats the #include lists for the
relevant files, which again is a token of the validate functions not
belonging where they were put.

3. There's probably room to share code across the different validators;
but this design isn't very amenable to that.

A comparison point worth noting is that the amcostestimate functions
are in more or less the same boat: they aren't part of the index
implementation in any meaningful way, but are really part of the
planner instead. Those are all in selfuncs.c, not under backend/access
at all.

There are a couple of things we could do instead:

* Put each amvalidate function into its own file (but probably keep it
in the same directory as now). This is a reasonable response to
points #1 and #2 but isn't very much help for #3.

* Collect the amvalidate functions into one file, which then leaves
us wondering where to put that; surely not under any one AM's directory.
A new file in src/backend/access/index/ is one plausible solution.
This file would also be a reasonable place to put the amvalidate()
dispatch function itself.

I'm somewhat leaning to the second choice, but perhaps someone has
a better idea, or an argument against doing that.

regards, tom lane