Re: WIP: BRIN multi-range indexes

I've pushed the first couple patches, reworking the BRIN interface and
the two existing opclasses. Attached are are the remaining bits,
implementing the two new opclasses.

0001 fixes the opckeytype I explained in the previous message. I'll
start a new thread, so that it does not get buried in this thread.

The 0002 and 0003 are the "main" patches, implementing all the stuff as
in-core opclasses. These patches were reviewed multiple times before, no
new changes.

0004 and 0005 are the patches moving the new opclasses to contrib. This
should also undo the catversion and OID generation changes from 0002 and
0003, but I'll take care of that if we actually decide contrib is the
right way. I kinda like it, if we can solve the two issues:

1) the opckeytype - I think this is a bug elsewhere, affecting any
opclass created by CREATE OPERATOR CLASS and not by directly injecting
the data into catalogs. I'll start a separate thread for that.

2) the pageinspect - Without knowing OID of the types used for summary,
brin_page_items can't print info about the bloom filter, minmax-multi
ranges, etc. Unfortunately, by moving the code to contrib we lose the
static OID assignment. I think there are three solutions to this:

a) Just use BYTEAOID, and accept that pageinspect prints just and
incomprehensible stream of characters

b) Use TypenameGetTypidExtended() to lookup the type by name. This is
what the code does now, but I'm afraid this might have security issues
due to search_path shenanigans. Base types can be created only by
superusers, but it's possible to create a composite type, and confuse
the lookup ...

c) Don't bother passing OID, and instead pass a pointer to the output
function directly. We'd need to extend BrinOpcInfo a bit, but that seems
like the simplest solution.

I think (b) is too dangerous/fragile, (a) is the simplest and (c) is a
bit too invasive/ugly I think.

regards

--
Tomas Vondra
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