I didn't consider them to be important as they showed the same, only the execution time was different. Also, they are a bit more complex than the ones put in the previous post. But here they are:
Definitions: ----------------------------------------------------------- CREATE OR REPLACE FUNCTION appfunctions.fnc_unit_conversion_factor(_tree_id integer, _unit_to_id integer) RETURNS real AS $BODY$ DECLARE BEGIN RETURN (SELECT unit_conv_factor AS factor FROM vew_unit_conversions AS c INNER JOIN tbl_sensors AS s ON (s.unit_id = c.unit_id_from) INNER JOIN tbl_trees USING (sens_id) WHERE tree_id = _tree_id AND unit_id_to = _unit_to_id)::real; END; $BODY$ LANGUAGE 'plpgsql' IMMUTABLE -------------------------- CREATE OR REPLACE FUNCTION appfunctions.fnc_unit_conversion_offset(_tree_id integer, _unit_to_id integer) RETURNS real AS $BODY$ DECLARE BEGIN RETURN (SELECT unit_conv_offset AS offset FROM vew_unit_conversions AS c INNER JOIN tbl_sensors AS s ON (s.unit_id = c.unit_id_from) INNER JOIN tbl_trees USING (sens_id) WHERE tree_id = _tree_id AND unit_id_to = _unit_to_id)::real; END; $BODY$ LANGUAGE 'plpgsql' IMMUTABLE -------------------------- CREATE OR REPLACE FUNCTION appfunctions.fnc_unit_convert(_rawdata real, _tree_id integer, _unit_to_id integer) RETURNS real AS $BODY$ DECLARE BEGIN RETURN _rawdata * fnc_unit_conversion_factor(_tree_id, _unit_to_id) + fnc_unit_conversion_offset(_tree_id, _unit_to_id); END; $BODY$ LANGUAGE 'plpgsql' IMMUTABLE Executions: ----------------------------------------------------------- EXPLAIN ANALYSE SELECT timestamp, data_from_tree_id_70 AS "flow_11" FROM (SELECT sens_chan_data_timestamp AS timestamp, sens_chan_data_data AS data_from_tree_id_70 FROM tbl_sensor_channel_data WHERE tree_id = 70 AND sens_chan_data_timestamp >= '2008-06-11T00:00:00' AND sens_chan_data_timestamp <= '2008-06-18T00:00:00' ) AS "70" ORDER BY timestamp; "Sort (cost=175531.00..175794.64 rows=105456 width=12) (actual time=598.454..638.400 rows=150678 loops=1)" " Sort Key: tbl_sensor_channel_data.sens_chan_data_timestamp" " Sort Method: external sort Disk: 3240kB" " -> Bitmap Heap Scan on tbl_sensor_channel_data (cost=3005.29..166732.66 rows=105456 width=12) (actual time=34.810..371.099 rows=150678 loops=1)" " Recheck Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" " -> Bitmap Index Scan on tbl_sensor_channel_data_pkey (cost=0.00..2978.92 rows=105456 width=0) (actual time=28.008..28.008 rows=150678 loops=1)" " Index Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" "Total runtime: 663.478 ms" ----------------------------------------------------------- EXPLAIN ANALYSE SELECT timestamp, fnc_unit_convert(data_from_tree_id_70, 70, 7) AS "flow_11" FROM (SELECT sens_chan_data_timestamp AS timestamp, sens_chan_data_data AS data_from_tree_id_70 FROM tbl_sensor_channel_data WHERE tree_id = 70 AND sens_chan_data_timestamp >= '2008-06-11T00:00:00' AND sens_chan_data_timestamp <= '2008-06-18T00:00:00' ) AS "70" ORDER BY timestamp; "Sort (cost=201895.00..202158.64 rows=105456 width=12) (actual time=35334.017..35372.977 rows=150678 loops=1)" " Sort Key: tbl_sensor_channel_data.sens_chan_data_timestamp" " Sort Method: external sort Disk: 3240kB" " -> Bitmap Heap Scan on tbl_sensor_channel_data (cost=3005.29..193096.66 rows=105456 width=12) (actual time=60.012..35037.129 rows=150678 loops=1)" " Recheck Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" " -> Bitmap Index Scan on tbl_sensor_channel_data_pkey (cost=0.00..2978.92 rows=105456 width=0) (actual time=21.884..21.884 rows=150678 loops=1)" " Index Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" "Total runtime: 35397.841 ms" ----------------------------------------------------------- EXPLAIN ANALYSE SELECT timestamp, data_from_tree_id_70*fnc_unit_conversion_factor(70, 7)+ fnc_unit_conversion_offset(70, 7) AS "flow_11" FROM (SELECT sens_chan_data_timestamp AS timestamp, sens_chan_data_data AS data_from_tree_id_70 FROM tbl_sensor_channel_data WHERE tree_id = 70 AND sens_chan_data_timestamp >= '2008-06-11T00:00:00' AND sens_chan_data_timestamp <= '2008-06-18T00:00:00' ) AS "70" ORDER BY timestamp; EXPLAIN ANALYSE SELECT timestamp, "Sort (cost=176058.28..176321.92 rows=105456 width=12) (actual time=630.350..669.843 rows=150678 loops=1)" " Sort Key: tbl_sensor_channel_data.sens_chan_data_timestamp" " Sort Method: external sort Disk: 3240kB" " -> Bitmap Heap Scan on tbl_sensor_channel_data (cost=3005.29..167259.94 rows=105456 width=12) (actual time=35.498..399.726 rows=150678 loops=1)" " Recheck Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" " -> Bitmap Index Scan on tbl_sensor_channel_data_pkey (cost=0.00..2978.92 rows=105456 width=0) (actual time=27.433..27.433 rows=150678 loops=1)" " Index Cond: ((tree_id = 70) AND (sens_chan_data_timestamp >= '2008-06-11 00:00:00'::timestamp without time zone) AND (sens_chan_data_timestamp <= '2008-06-18 00:00:00'::timestamp without time zone))" "Total runtime: 694.968 ms" "Szymon Guz" <mabew...@gmail.com> wrote in message news:aanlktimb8-0kzrrbddqgxnz5tjdgf2t3ffbu2lvx-...@mail.gmail.com... 2010/6/19 Davor J. <dav...@live.com> I think I have read what is to be read about queries being prepared in plpgsql functions, but I still can not explain the following, so I thought to post it here: Suppose 2 functions: factor(int,int) and offset(int, int). Suppose a third function: convert(float,int,int) which simply returns $1*factor($2,$3)+offset($2,$3) All three functions are IMMUTABLE. Very simple, right? Now I have very fast AND very slow executing queries on some 150k records: VERY FAST (half a second): ---------------- SELECT data*factor(1,2)+offset(1,2) FROM tbl_data; VERY SLOW (a minute): ---------------- SELECT convert(data, 1, 2) FROM tbl_data; The slowness cannot be due to calling a function 150k times. If I define convert2(float,int,int) to return a constant value, then it executes in about a second. (still half as slow as the VERY FAST query). I assume that factor and offset are cached in the VERY FAST query, and not in the slow one? If so, why not and how can I "force" it? Currently I need only one function for conversions. Regards, Davor Hi, show us the code of those two functions and explain analyze of those queries. regards Szymon Guz
