Hello if you read a some longer field - longer than 2Kb, then PostgreSQL has to read this value from a table_toast file. see http://developer.postgresql.org/pgdocs/postgres/storage-toast.html - and reading have to be slower than you don't read this field. Regards Pavel Stehule 2010/8/29 Volodymyr Kostyrko <c.kworr@xxxxxxxxx>: > I don't clearly understand why this happens, but when I try join some tables > using arrays I end up with: > > =# explain select count(*) from urls JOIN rules ON urls.tag && rules.tag; > QUERY PLAN > --------------------------------------------------------------------------------------- > Aggregate (cost=1356.27..1356.28 rows=1 width=0) > -> Nested Loop (cost=20.33..1354.96 rows=523 width=0) > -> Seq Scan on rules (cost=0.00..1.01 rows=1 width=37) > -> Bitmap Heap Scan on urls (cost=20.33..1347.42 rows=523 > width=29) > Recheck Cond: (urls.tag && rules.tag) > -> Bitmap Index Scan on url_tag_g (cost=0.00..20.20 rows=523 > width=0) > Index Cond: (urls.tag && rules.tag) > > Here tag is text[] with list of tags. Whole select takes 142 ms. It drops > down to 42 ms when I add some conditions that strip result table to zero > length. > > What am I missing? Is there any other ways to overlap those ones? Or should > I find "any other way"? > > -- > Sphinx of black quartz judge my vow. > > -- > Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance > -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
