Subject: Re: coupling of index and table access methods

From: Aleksey Demakov <[email-masked]>
Date: Wed, 2 Oct 2024 08:07:06 +0300

As far as I see a possible way to do this is to add two optional
functions to table AM interface:

char * (*default_index_am)(void) ;
bool (*validate_index_am)(char *);

If the first one is not provided then DEFAULT_INDEX_TYPE, that is
"btree", has to be used instead. If the second one is not provided
then this as if it always returned true.

But in other places DEFAULT_INDEX_TYPE should be replaced with
invocation of (table_am->default_index_am)(). This is not always
possible directly, e.g. we don't yet have the table_am here:

access_method_clause:
            USING name                                { $$ = $2; }
            | /*EMPTY*/                                { $$ =
DEFAULT_INDEX_TYPE; }
        ;

So in places like this some placeholder has to be used instead which
would be replaced with a real thing at some later point.

Regards,
Aleksey

On Tue, Oct 1, 2024 at 4:51 PM Aleksey Demakov <[email-masked]> wrote:
>
> Hi hackers,
>
> My extension introduces a new table access method together with an
> index access method. Specifically, these AMs work with in-memory data.
>
> I would like to make a CREATE TABLE request with PRIMARY KEY, UNIQUE
> constraints etc, to pick my in-memory index AM over default btree when
> the table is created using my in-memory table AM. Also it might make
> sense to forbid using other index AM for CREATE INDEX requests against
> an in-memory table.
>
> It seems that this is not possible now without modifying the psql
> core. What might be the best way to accomplish this?
>
> Also if I implement such a thing would anybody else be interested in
> it? Is there any sense to publish it?
>
> Regards,
> Aleksey