Re: Bad row estimates

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Otherwise I think you really need a special datatype for time
> intervals and a GIST or r-tree index on it :-(.

You could actually take short cuts using expression indexes to do this. If it
works out well then you might want to implement a real data type to avoid the
overhead of the SQL conversion functions.

Here's an example. If I were to do this for real I would look for a better
datatype than the box datatype and I would wrap the whole conversion in an SQL
function. But this will serve to demonstrate:

stark=> create table interval_test (start_ts timestamp with time zone, end_ts timestamp with time zone);
CREATE TABLE

stark=> create index interval_idx on interval_test using gist (box(point(start_ts::abstime::integer, end_ts::abstime::integer) , point(start_ts::abstime::integer, end_ts::abstime::integer)));
CREATE INDEX

stark=> explain select * from interval_test where box(point(now()::abstime::integer,now()::abstime::integer),point(now()::abstime::integer,now()::abstime::integer)) ~ box(point(start_ts::abstime::integer, end_ts::abstime::integer) , point(start_ts::abstime::integer, end_ts::abstime::integer));
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Index Scan using interval_idx on interval_test (cost=0.07..8.36 rows=2 width=16)
Index Cond: (box(point((((now())::abstime)::integer)::double precision, (((now())::abstime)::integer)::double precision), point((((now())::abstime)::integer)::double precision, (((now())::abstime)::integer)::double precision)) ~ box(point((((start_ts)::abstime)::integer)::double precision, (((end_ts)::abstime)::integer)::double precision), point((((start_ts)::abstime)::integer)::double precision, (((end_ts)::abstime)::integer)::double precision)))
(2 rows)

--
greg