Re: Dump/Restore of non-default PKs

At the moment you cannot create a unique index other than a btree. (As
discussed on other threads, I am pursuing unique hash indexes for
PostgreSQL, one step at a time).
You get "ERROR index foo_idx is not a btree"

According to parse_utilcmd.c line 2310, this is because it would break
pg_dump, which needs ADD CONSTRAINT to create the same kind of index
again. Fair enough.

This is needed because ADD CONSTRAINT just uses the defaults index
type. We could simply allow a GUC for
default_primary_key_access_method, but that is overkill and there
seems to be an easy and more general solution:

I propose that we change pg_dump so that when it creates a PK it does
so in 2 commands:
1. CREATE [UNIQUE] INDEX iname ...
2. ALTER TABLE .. ADD PRIMARY KEY USING INDEX iname;

Step
(1) recreates the index, respecting its AM, even if that is not a btree
(2) works and there is no problem with defaults

Doing this as 2 steps instead of one doesn't add any more time because
(2) is just a metadata-only change, not an index build.

Any objections to a patch to implement this thought?