Re: jsonb array-style subscription

On Thu, Mar 3, 2016 at 2:31 AM, Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote:
> Well, actually, I agree with that. I can try to rework the patch to achieve
> this goal.

Good idea.

I wonder, having taken a quick look at the patch, how this works?:

+select * from test_jsonb_subscript where
test_json['key_doesnt_exists'] = '"value"';
+ id | test_json
+----+-----------
+(0 rows)

Can this use an index, in principle? If not, do you have a plan to get
it to a place where it can? How can the expression be made to map on
to existing indexable operators, such as the containment operator @>,
or even B-Tree opclass operators like = or <=, for example?

This kind of thing was always my main problem with jsonb array-style
subscription. I think it's really quite desirable in theory, but I
also think that these problems need to be fixed first. Think that I
made this point before.

ISTM that these expressions need to be indexable in some way, which
seems like a significantly harder project, especially because the
mapping between an expression in a predicate like this and an
indexable operator like @> is completely non-obvious. Making such a
mapping itself extensible seems even more tricky, which is what it
would take, I suspect. Indexing is always of great importance for
jsonb. It's already too complicated.

--
Peter Geoghega