Re: Why date index is not used

[Tomas Vondra <tv(at)fuzzy(dot)cz>]

If you want to benefit from the usage of an index, the query has to
contain some WHERE conditions (on the indexed columns). This is a
'select all' query - there is no way to speed it up using index.

Tomas

> > Why Postgres 8.1 does not use makse_kuupaev_idx index in the
following query
> > ?
> >
> > How to speed this query up ?
> >
> > explain analyze select * from makse order by kuupaev desc, kellaaeg
desc
> > limit 100
> >
> > "Limit  (cost=62907.94..62908.19 rows=100 width=876) (actual
> > time=33699.551..33701.001 rows=100 loops=1)"
> > "  ->  Sort  (cost=62907.94..63040.49 rows=53022 width=876) (actual
> > time=33699.534..33700.129 rows=100 loops=1)"
> > "        Sort Key: kuupaev, kellaaeg"
> > "        ->  Seq Scan on makse  (cost=0.00..2717.22 rows=53022
width=876)
> > (actual time=0.020..308.502 rows=53028 loops=1)"
> > "Total runtime: 37857.177 ms"
> >
> >
> > CREATE TABLE makse(
> >   kuupaev date,
> >   kellaaeg char(6) NOT NULL DEFAULT ''::bpchar,
> >   guid char(36) NOT NULL,
> >   CONSTRAINT makse_pkey PRIMARY KEY (guid) )
> >
> >
> > CREATE INDEX makse_kuupaev_idx  ON makse  USING btree  (kuupaev);