I seem to have some planner oddity, where it seems to completely
mispredict the output after a regex compare. I've seem it on other
occasions, where it completely screws up the join. You can note the
"rows=1" after the filter.
A similar sitution has occurred when doing a regex filter in a subquery,
which was subsequently predited as 1 row and triggered (oddly enough) a
sequencial scan. Doing the same using "equality" on the result to
substring(<text> from <regex>) seemed to work and produced a useful
plan, since it did a hash-join (as it should have).
Is this a known problem? Otherwise I think I should build a smaller test
case...
Using Postgresql 8.2.6 from Debian Etch-backports.
"Bitmap Heap Scan on log_syslog syslog (cost=13124.26..51855.25 rows=1
width=270)"
" Recheck Cond: (((program)::text = 'amavis'::text) AND
((facility)::text = 'mail'::text))"
" Filter: ***SOME VERY LONG SIMILAR TO REGEX****"
" -> BitmapAnd (cost=13124.26..13124.26 rows=18957 width=0)"
" -> Bitmap Index Scan on "IX_log_syslog_program"
(cost=0.00..2223.95 rows=92323 width=0)"
" Index Cond: ((program)::text = 'amavis'::text)"
" -> Bitmap Index Scan on "IX_log_syslog_facility"
(cost=0.00..10899.81 rows=463621 width=0)"
" Index Cond: ((facility)::text = 'mail'::text)"
- Joris