On 21/07/2012 00:10, Tom Lane wrote:
Claudio Freire <klaussfreire@xxxxxxxxx> writes:
Looking at this:
" -> Index Scan using
idx_message_copies_wk2_date_src_pos_partial on message_copies_wk2
message_copies (cost=0.00..19057.93 rows=52 width=32) (actual
time=62.124..5486270.845 rows=387524 loops=1)"
" Index Cond: ((date_trunc('day'::text,
msg_date_rec) = '2012-07-17 00:00:00'::timestamp without time zone)
AND (src_id = 1))"
" Filter: ((date_part('day'::text,
msg_date_rec) = 17::double precision) AND (NOT (((((pos_georef1)::text
|| (pos_georef2)::text) || (pos_georef3)::text) ||
(pos_georef4)::text) IS NULL)) AND (((((pos_georef1)::text ||
(pos_georef2)::text) || (pos_georef3)::text) || (pos_georef4)::text)
<> ''::text))"
I think the real problem is that the planner has no hope of doing
anything very accurate with such an unwieldy filter condition. I'd look
at ways of making the filter conditions simpler, perhaps by recasting
the data representation. In particular, that's a horridly bad way of
asking whether some columns are empty, which I gather is the intent.
If you really want to do it just like that, creating an index on the
concatenation expression would guide ANALYZE to collect some stats about
it, but it would probably be a lot more efficient to put together an AND
or OR of tests on the individual columns.
regards, tom lane
So what you suggest is to forget all together the concatenation of the
georef1/2/3/4 and instead alter my query with something like:
georef1 is not null and not georeg1 = ''....etc for georef2 3 and 4
That would require to alter my index and have the four georef columns
separately in it and not as a concatenation and so on for the partial
index part. And a final thing, you seem to imply that the indexes are
used by the analyser to collect statistics even if they are not used. So
an index serves not only as a way to speed up targeted queries but also
to provide better statistics to the analyzer?
Kind Regards
Yiannis
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