Constraint exclusion for timestamp expression

[Victor Yegorov <vyegorov@xxxxxxxxx>]

Greetings.

I have a partitioned table, that can be reproduced the following way:

CREATE TABLE ara (

    ara_id      int4,

    name        varchar(11),

    run_id      int4,

    set_id      int4,

    created_at  timestamp,

    CONSTRAINT p_ara PRIMARY KEY (ara_id)

);

DO $partition$

DECLARE

    _tab    text;

    _mon    timestamp;

BEGIN

    FOR _mon IN

        SELECT * FROM generate_series('2013-10-01'::timestamp, date_trunc('mon',now()+interval'2mon'),interval'1mon') s(dt)

    LOOP

        _tab:='ara_'||to_char(_mon, 'YYYYMM');

        RAISE NOTICE '..oO( Creating % )', _tab;

        EXECUTE format($$CREATE TABLE %I (CONSTRAINT c_ara_partition CHECK (created_at >= %L AND created_at < %L)) INHERITS (ara)$$,

                             _tab, _mon, (_mon+interval'1mon'));

        EXECUTE format($$CREATE UNIQUE INDEX p_%s ON %I(ara_id)$$, _tab, _tab);

        EXECUTE format($$CREATE INDEX i_%s_name ON %I(name)$$, _tab, _tab);

        EXECUTE format($$CREATE INDEX i_%s_run_and_name ON %I(run_id,name)$$, _tab, _tab);

    END LOOP;

END;

$partition$;

Now, if I check plan for this query:

EXPLAIN SELECT * FROM ara

 WHERE ara.created_at

       BETWEEN (current_timestamp-interval'90 days')::timestamp

           AND (current_timestamp)::timestamp;

I can see that all partitions are considered by the planner.

If I replace the interval _expression_ with constant, like this:

EXPLAIN SELECT * FROM ara

 WHERE ara.created_at

       BETWEEN '2014-02-20'::timestamp

           AND (current_timestamp)::timestamp;

then partition pruning kicks in and skips outdated partitions. The same happens for the future-dated partitions if I use a constant timestamp for the upper limit.

`constraint_exclusion` is default: partition

This happens on 9.1.13, but I get the same plans also on 9.3.4.

How can I enforce pruning to kick in for the initial expressions?

--
Victor Y. Yegorov