On 04/09/2014 10:40 AM, Peter Geoghegan wrote:
On Tue, Apr 8, 2014 at 11:37 PM, Heikki Linnakangas
<hlinnakan...@vmware.com> wrote:
As the code stands, you don't have a choice on any of those things. The
decisions have been made by us, PostgreSQL developers. The only choice you
have is between jsonb_ops and jsonb_hash_ops, with a strange combination of
tradeoffs in both. Sure, they're still useful, if not optimal, for a
wide-range of applications. For more complicated cases, you will have to
resort to expression indexes. It bugs me greatly that the underlying indexam
could do all those things, we're just not exposing the capability.

Why would you ever not have to use expression indexes? Idiomatic usage
of jsonb involves expression indexes because it's desirable to index
only a expression. People will want to do things like only index the
nested "tags" array far more frequently then they'll only want to
index keys (that is, Object pair keys) in the entire document. I don't
get why you'd say that they'd "resort" to expression indexes, like
they're a kludge.

Expression indexes are definitely nice, but you have to be careful to formulate the query in exactly the same way to match the index.

Have you ever tried out one of the new document
databases? I suggest you do. Expression indexes on jsonb map pretty
closely onto how you're frequently expected to index data in those
systems. That's something that they make heavy use of. Why would you
ever not really have to consider ahead of time what is important
enough to be indexed, and what is not?

I didn't say that. On the contrary, I think the shotgun approach jsonb_ops and jsonb_hash_ops take is too broad. It should be possible to specify what to index in a more detailed fashion.

- Heikki

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