Re: [PERFORM] timestamp with time zone

[Alessandro Gagliardi]

I tried: CREATE INDEX blocks_created_at_timezone_idx ON blocks USING btree
((created at time zone timezone));

(Actually, I originally did try one on "(created at time zone
timezone)::date" but couldn't figure out how to phrase it in a way
PostgreSQL would accept.)

Anyway, no difference: http://explain.depesz.com/s/Zre

I even tried changing the filter to (created at time zone timezone) >
 'yesterday' AND (created at time zone timezone) < 'today' to see if that
might make a difference. Sadly, no: http://explain.depesz.com/s/dfh

Here's the definition for the offending table:

CREATE TABLE blocks
(
  block_id character(24) NOT NULL,
  user_id character(24) NOT NULL,
  created timestamp with time zone,
  locale character varying,
  shared boolean,
  private boolean,
  moment_type character varying NOT NULL,
  user_agent character varying,
  inserted timestamp without time zone NOT NULL DEFAULT now(),
  networks character varying[],
  lnglat point,
  timezone character varying,
  CONSTRAINT blocks_pkey PRIMARY KEY (block_id )
)
WITH (
  OIDS=FALSE
);

CREATE INDEX blocks_created_at_timezone_idx
  ON blocks
  USING btree
  (timezone(timezone::text, created) );

CREATE INDEX blocks_created_idx
  ON blocks
  USING btree
  (created  DESC NULLS LAST);

CREATE INDEX blocks_lnglat_idx
  ON blocks
  USING gist
  (lnglat );

CREATE INDEX blocks_moment_type_idx
  ON blocks
  USING btree
  (moment_type );

CREATE INDEX blocks_networks_idx
  ON blocks
  USING btree
  (networks );

CREATE INDEX blocks_private_idx
  ON blocks
  USING btree
  (private );

CREATE INDEX blocks_shared_idx
  ON blocks
  USING btree
  (shared );

CREATE INDEX blocks_timezone_idx
  ON blocks
  USING btree
  (timezone );


On Thu, Feb 9, 2012 at 11:46 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:

> Alessandro Gagliardi <alessan...@path.com> writes:
> > WHERE ... (created at time zone timezone)::date = 'yesterday'
>
> > created has an index (btree if it matters). timezone does not. I'm
> > wondering if the solution to my problem is to create a joint index
> between
> > created and timezone (and if so, if there is a particular way to do that
> to
> > make it work the way I want).
>
> The only way to make that indexable is to create an expression index on
> the whole expression "(created at time zone timezone)::date".  Seems
> pretty special-purpose, though it might be worthwhile if you do that a
> lot.
>
>                        regards, tom lane
>