![functions=# set track_functions = 'pl';
SET
functions=# select * from pg_stat_user_functions;
(No rows)
functions=# SELECT count(*) FROM bird_strikes ...
-[ RECORD 1 ]
count | 850
Track Function Usage](https://image.slidesharecdn.com/postgresqlfunctions-150224190325-conversion-gate01/85/PostgreSQL-Procedural-Languages-Tips-Tricks-and-Gotchas-8-320.jpg)
![functions=# select * from pg_stat_user_functions;
-[ RECORD 1 ]----------------------------
funcid | 41247
schemaname | public
funcname | get_iata_code_from_name
calls | 88547
total_time | 12493.419
self_time | 12493.419
-[ RECORD 2 ]----------------------------
funcid | 41246
schemaname | public
funcname | get_iata_code_from_abbr_name
calls | 99404
total_time | 13977.674
self_time | 1484.255
Isolate Performance Issues](https://image.slidesharecdn.com/postgresqlfunctions-150224190325-conversion-gate01/85/PostgreSQL-Procedural-Languages-Tips-Tricks-and-Gotchas-9-320.jpg)
![PL/TCL
CREATE FUNCTION empty_tcl_trigger()
RETURNS trigger AS
$$
return [array get NEW]
$$ LANGUAGE pltcl;](https://image.slidesharecdn.com/postgresqlfunctions-150224190325-conversion-gate01/85/PostgreSQL-Procedural-Languages-Tips-Tricks-and-Gotchas-38-320.jpg)
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PostgreSQL Procedural Languages: Tips, Tricks and Gotchas
- 1. PostgreSQL Procedural Languages: Tips, Tricks & Gotchas
- 2. Who Am I? ● Jim Mlodgenski – [email protected] – @jim_mlodgenski ● Co-organizer of – NYC PUG (www.nycpug.org) – Philly PUG (www.phlpug.org) ● CTO, OpenSCG – www.openscg.com
- 4. Stored procedures/functions ● Code that runs inside of the database ● Used for: – Performance – Security – Convenience
- 5. functions=# SELECT airport FROM bird_strikes LIMIT 5; airport -------------------------- NEWARK LIBERTY INTL ARPT UNKNOWN DENVER INTL AIRPORT CHICAGO O'HARE INTL ARPT JOHN F KENNEDY INTL (5 rows) Source: http://wildlife.faa.gov/ Sample Data
- 6. functions=# SELECT count(*) functions-# FROM bird_strikes functions-# WHERE get_iata_code_from_abbr_name(airport) = 'LAX'; count ------- 850 (1 row) Time: 13490.611 ms Data Formatting Functions
- 7. functions=# EXPLAIN ANALYZE SELECT count(*) FROM bird_strikes ... QUERY PLAN ------------------------------------------------------------------------ Aggregate (cost=29418.79..29418.80 rows=1 width=0) (actual time=13463.628..13463.629 rows=1 loops=1) -> Seq Scan on bird_strikes (cost=0.00..29417.55 rows=497 width=0) (actual time=15.721..13463.293 rows=850 loops=1) Filter: ((get_iata_code_from_abbr_name(airport))::text = 'LAX'::text) Rows Removed by Filter: 98554 Planning time: 0.124 ms Execution time: 13463.682 ms (6 rows) Check Performance
- 8. functions=# set track_functions = 'pl'; SET functions=# select * from pg_stat_user_functions; (No rows) functions=# SELECT count(*) FROM bird_strikes ... -[ RECORD 1 ] count | 850 Track Function Usage
- 9. functions=# select * from pg_stat_user_functions; -[ RECORD 1 ]---------------------------- funcid | 41247 schemaname | public funcname | get_iata_code_from_name calls | 88547 total_time | 12493.419 self_time | 12493.419 -[ RECORD 2 ]---------------------------- funcid | 41246 schemaname | public funcname | get_iata_code_from_abbr_name calls | 99404 total_time | 13977.674 self_time | 1484.255 Isolate Performance Issues
- 10. CREATE OR REPLACE FUNCTION get_iata_code_from_abbr_name(abbr_name varchar) RETURNS varchar AS $$ DECLARE working_name varchar; code varchar := null; BEGIN working_name := upper(abbr_name); IF working_name = 'UNKNOWN' THEN RETURN null; END IF; working_name := replace(working_name, 'INTL', 'INTERNATIONAL'); working_name := replace(working_name, 'ARPT', 'AIRPORT'); working_name := replace(working_name, 'MUNI', 'MUNICIPAL'); working_name := replace(working_name, 'METRO', 'METROPOLITAN'); working_name := replace(working_name, 'NATL', 'NATIONAL'); working_name := replace(working_name, '-', ' '); working_name := replace(working_name, '/', ' '); working_name := working_name || '%'; code := get_iata_code_from_name(working_name); RETURN code; END; $$ LANGUAGE plpgsql;
- 11. CREATE OR REPLACE FUNCTION get_iata_code_from_name(airport_name varchar) RETURNS varchar AS $$ DECLARE working_name varchar; code varchar := null; BEGIN working_name := upper(airport_name); EXECUTE $__$ SELECT iata_code FROM airports WHERE upper(name) LIKE $1 $__$ INTO code USING working_name; RETURN code; END; $$ LANGUAGE plpgsql;
- 13. functions=# select * from pl_profiler ; func_oid | line_number | line | exec_count | total_time | longest_time ----------+-------------+---------------------------------------------------------------------+------------+------------+-------------- 41246 | 1 | | 0 | 0 | 0 41246 | 2 | DECLARE | 0 | 0 | 0 41246 | 3 | working_name varchar; | 0 | 0 | 0 41246 | 4 | code varchar := null; | 0 | 0 | 0 41246 | 5 | BEGIN | 0 | 0 | 0 41246 | 6 | working_name := upper(abbr_name); | 99404 | 210587 | 363 41246 | 7 | | 0 | 0 | 0 41246 | 8 | IF working_name = 'UNKNOWN' THEN | 99404 | 63406 | 97 41246 | 9 | RETURN null; | 10857 | 2744 | 15 41246 | 10 | END IF; | 0 | 0 | 0 41246 | 11 | | 0 | 0 | 0 41246 | 12 | working_name := replace(working_name, 'INTL', 'INTERNATIONAL'); | 88547 | 116474 | 145 41246 | 13 | working_name := replace(working_name, 'ARPT', 'AIRPORT'); | 88547 | 83015 | 91 41246 | 14 | working_name := replace(working_name, 'MUNI', 'MUNICIPAL'); | 88547 | 70676 | 74 41246 | 15 | working_name := replace(working_name, 'METRO', 'METROPOLITAN'); | 88547 | 67392 | 63 41246 | 16 | working_name := replace(working_name, 'NATL', 'NATIONAL'); | 88547 | 64681 | 70 41246 | 17 | | 0 | 0 | 0 41246 | 18 | working_name := replace(working_name, '-', ' '); | 88547 | 66771 | 62 41246 | 19 | working_name := replace(working_name, '/', ' '); | 88547 | 65054 | 66 41246 | 20 | working_name := working_name || '%'; | 88547 | 64892 | 207 41246 | 21 | | 0 | 0 | 0 41246 | 22 | code := get_iata_code_from_name(working_name); | 88547 | 12282997 | 3709 41246 | 23 | | 0 | 0 | 0 41246 | 24 | RETURN code; | 88547 | 33374 | 14 41246 | 25 | END; | 0 | 0 | 0 41247 | 1 | | 0 | 0 | 0 41247 | 2 | DECLARE | 0 | 0 | 0 41247 | 3 | working_name varchar; | 0 | 0 | 0 41247 | 4 | code varchar := null; | 0 | 0 | 0 41247 | 5 | BEGIN | 0 | 0 | 0 41247 | 6 | working_name := upper(airport_name); | 88547 | 170273 | 90 41247 | 7 | | 0 | 0 | 0 41247 | 8 | EXECUTE $__$ SELECT iata_code | 88547 | 11572604 | 3273 41247 | 9 | FROM airports | 0 | 0 | 0 41247 | 10 | WHERE upper(name) LIKE $1 | 0 | 0 | 0 41247 | 11 | $__$ | 0 | 0 | 0 41247 | 12 | INTO code | 0 | 0 | 0 41247 | 13 | USING working_name; | 0 | 0 | 0 41247 | 14 | | 0 | 0 | 0 41247 | 15 | RETURN code; | 88547 | 121574 | 27 41247 | 16 | END; | 0 | 0 | 0 (41 rows) Profiler https://bitbucket.org/openscg/plprofiler
- 14. ● Be careful when you have a function call another function – May lead to difficult to diagnose performance problems ● Be careful when a function is used in a WHERE clause – For sequential scans, it may execute once per row in the table
- 15. functions=# SELECT iso_region FROM airports LIMIT 5; iso_region ------------ US-PA US-AK US-AL US-AR US-AZ (5 rows) Source: http://ourairports.com/data/ Sample Data
- 16. CREATE TYPE airport_regions AS (airport_name varchar, airport_continent varchar, airport_country varchar, airport_state varchar); CREATE OR REPLACE FUNCTION get_airport_regions() RETURNS SETOF airport_regions AS $$ BEGIN RETURN QUERY SELECT name::varchar, continent::varchar, iso_country::varchar, split_part(iso_region, '-', 2)::varchar FROM airports; END; $$ LANGUAGE plpgsql; Set Returning Functions
- 17. functions=# SELECT b.num_wildlife_struck FROM bird_strikes b, state_code s, get_airport_regions() r WHERE b.origin_state = s.name AND s.abbreviation = r.airport_state AND r.airport_continent = 'NA'; num_wildlife_struck --------------------- … Time: 48507.635 ms
- 18. QUERY PLAN ----------------------------------------------------------------------------------------------------------- Nested Loop (cost=42.10..318.77 rows=1972 width=2) (actual time=43.468..38467.229 rows=60334427 loops=1) -> Hash Join (cost=12.81..14.51 rows=1 width=9) (actual time=43.284..58.007 rows=21488 loops=1) Hash Cond: ((s.abbreviation)::text = (r.airport_state)::text) -> Seq Scan on state_code s (cost=0.00..1.50 rows=50 width=12) (actual time=0.007..0.045 rows=50 loops=1) -> Hash (cost=12.75..12.75 rows=5 width=32) (actual time=43.264..43.264 rows=25056 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 857kB -> Function Scan on get_airport_regions r (cost=0.25..12.75 rows=5 width=32) (actual time=34.050..39.650 rows=25056 loops=1) Filter: ((airport_continent)::text = 'NA'::text) Rows Removed by Filter: 21150 -> Bitmap Heap Scan on bird_strikes b (cost=29.29..288.48 rows=1578 width=10) (actual time=0.445..1.343 rows=2808 loops=21488) Recheck Cond: ((origin_state)::text = (s.name)::text) Heap Blocks: exact=31639334 -> Bitmap Index Scan on bird_strikes_state (cost=0.00..28.89 rows=1578 width=0) (actual time=0.285..0.285 rows=2808 loops=21488) Index Cond: ((origin_state)::text = (s.name)::text) Planning time: 0.742 ms Execution time: 40447.925 ms (16 rows) Time: 40449.209 ms
- 19. CREATE OR REPLACE FUNCTION get_airport_regions() RETURNS SETOF airport_regions AS $$ BEGIN RETURN QUERY SELECT name::varchar, continent::varchar, iso_country::varchar, split_part(iso_region, '-', 2)::varchar FROM airports; END; $$ LANGUAGE plpgsql ROWS 46206 COST 600000;
- 20. QUERY PLAN -------------------------------------------------------------------------------------------------------------- Hash Join (cost=2081.87..7687.83 rows=91120 width=2) (actual time=51.589..7568.729 rows=60334427 loops=1) Hash Cond: ((b.origin_state)::text = (s.name)::text) -> Seq Scan on bird_strikes b (cost=0.00..4318.04 rows=99404 width=10) (actual time=0.006..14.207 rows=99404 loops=1) -> Hash (cost=2081.15..2081.15 rows=58 width=9) (actual time=51.571..51.571 rows=21488 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 861kB -> Hash Join (cost=1502.12..2081.15 rows=58 width=9) (actual time=37.574..48.385 rows=21488 loops=1) Hash Cond: ((r.airport_state)::text = (s.abbreviation)::text) -> Function Scan on get_airport_regions r (cost=1500.00..2077.57 rows=231 width=32) (actual time=37.526..42.626 rows=25056 loops=1) Filter: ((airport_continent)::text = 'NA'::text) Rows Removed by Filter: 21150 -> Hash (cost=1.50..1.50 rows=50 width=12) (actual time=0.041..0.041 rows=50 loops=1) Buckets: 1024 Batches: 1 Memory Usage: 3kB -> Seq Scan on state_code s (cost=0.00..1.50 rows=50 width=12) (actual time=0.004..0.020 rows=50 loops=1) Planning time: 0.722 ms Execution time: 9572.353 ms (15 rows) Time: 9573.716 ms
- 21. ● When using set returning functions as tables, the row and cost estimates are usually way off – Default ROWS: 1000 – Default COST: 100 ● Note: COST is in units of cpu_operator_cost which is 0.0025
- 22. ● Do not use functions to mask a bad data model ● Use functions to help load the data into the correct format
- 23. Table Partitioning ● Usually done for performance ● Uses check constraints and inherited tables ● Triggers are preferred over rules so COPY can be used ● Trigger functions used to move the data to the correct child table
- 24. CREATE UNLOGGED TABLE trigger_test (key serial primary key, value varchar, insert_ts timestamp, update_ts timestamp); CREATE UNLOGGED TABLE trigger_test_0 (CHECK ( key % 5 = 0)) INHERITS (trigger_test); CREATE UNLOGGED TABLE trigger_test_1 (CHECK ( key % 5 = 1)) INHERITS (trigger_test); CREATE UNLOGGED TABLE trigger_test_2 (CHECK ( key % 5 = 2)) INHERITS (trigger_test); CREATE UNLOGGED TABLE trigger_test_3 (CHECK ( key % 5 = 3)) INHERITS (trigger_test); CREATE UNLOGGED TABLE trigger_test_4 (CHECK ( key % 5 = 4)) INHERITS (trigger_test);
- 25. CREATE OR REPLACE FUNCTION partition_trigger() RETURNS trigger AS $$ DECLARE partition int; BEGIN partition = NEW.key % 5; EXECUTE 'INSERT INTO trigger_test_' || partition || ' VALUES (($1).*)' USING NEW; RETURN NULL; END; $$ LANGUAGE plpgsql; CREATE TRIGGER partition_trigger BEFORE INSERT ON trigger_test FOR EACH ROW EXECUTE PROCEDURE partition_trigger(); Dynamic Trigger
- 26. CREATE OR REPLACE FUNCTION partition_trigger() RETURNS trigger AS $$ BEGIN CASE NEW.key % 5 WHEN 0 THEN INSERT INTO trigger_test_0 VALUES (NEW.*); WHEN 1 THEN INSERT INTO trigger_test_1 VALUES (NEW.*); WHEN 2 THEN INSERT INTO trigger_test_2 VALUES (NEW.*); WHEN 3 THEN INSERT INTO trigger_test_3 VALUES (NEW.*); WHEN 4 THEN INSERT INTO trigger_test_4 VALUES (NEW.*); END CASE; RETURN NULL; END; $$ LANGUAGE plpgsql; Case Statement
- 27. ● 16% performance gain using CASE Statement ● Tested inserting 100,000 rows Dynamic Trigger Case Trigger 3200 3400 3600 3800 4000 4200 4400 Performance of Partition Triggers
- 28. Trigger Overhead ● Triggers get executed when an event happens in the database – INSERT, UPDATE, DELETE ● Event Triggers fire on DDL – CREATE, DROP, ALTER
- 29. CREATE UNLOGGED TABLE trigger_test ( key serial primary key, value varchar, insert_ts timestamp, update_ts timestamp ); INSERTS.pgbench INSERT INTO trigger_test (value) VALUES (‘hello’);
- 30. pgbench -n -t 100000 -f INSERTS.pgbench functions Inserts: 5191 TPS
- 31. CREATE FUNCTION empty_trigger() RETURNS trigger AS $$ BEGIN RETURN NEW; END; $$ LANGUAGE plpgsql; CREATE TRIGGER empty_trigger BEFORE INSERT OR UPDATE ON trigger_test FOR EACH ROW EXECUTE PROCEDURE empty_trigger();
- 32. pgbench -n -t 100000 -f INSERTS.pgbench functions Inserts: 4906 TPS (5.5% overhead)
- 33. Overhead of PL Languages ● PL/pgSQL ● C ● PL/Perl ● PL/TCL ● PL/Python ● PL/v8 ● PL/Lua ● PL/R ● PL/sh
- 34. PL/pgSQL CREATE FUNCTION empty_trigger() RETURNS trigger AS $$ BEGIN RETURN NEW; END; $$ LANGUAGE plpgsql;
- 35. C #include "postgres.h" #include "commands/trigger.h" PG_MODULE_MAGIC; Datum empty_c_trigger(PG_FUNCTION_ARGS); PG_FUNCTION_INFO_V1(empty_c_trigger); Datum empty_c_trigger(PG_FUNCTION_ARGS) { TriggerData *tg; HeapTuple ret; tg = (TriggerData *) (fcinfo->context); if (TRIGGER_FIRED_BY_UPDATE(tg->tg_event)) ret = tg->tg_newtuple; else ret = tg->tg_trigtuple; return PointerGetDatum(ret); }
- 36. PL/Python CREATE FUNCTION empty_python_trigger() RETURNS trigger AS $$ return $$ LANGUAGE plpythonu;
- 37. PL/Perl CREATE FUNCTION empty_perl_trigger() RETURNS trigger AS $$ return; $$ LANGUAGE plperl;
- 38. PL/TCL CREATE FUNCTION empty_tcl_trigger() RETURNS trigger AS $$ return [array get NEW] $$ LANGUAGE pltcl;
- 39. PL/v8 CREATE FUNCTION empty_v8_trigger() RETURNS trigger AS $$ return NEW; $$ LANGUAGE plv8;
- 40. PL/R CREATE FUNCTION empty_r_trigger() RETURNS trigger AS $$ return(pg.tg.new) $$ LANGUAGE plr;
- 41. PL/Lua CREATE FUNCTION empty_lua_trigger() RETURNS trigger AS $$ return $$ LANGUAGE pllua;
- 42. PL/sh CREATE FUNCTION empty_sh_trigger() RETURNS trigger AS $$ #!/bin/sh exit 0 $$ LANGUAGE plsh;
- 43. C PL/pgSQL PL/Lua PL/Python PL/Perl PL/v8 PL/TCL PL/R PL/sh 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% Percent overhead of triggers
- 44. ● Think things through before adding server side code ● Performance test your functions ● Don't use a procedural language just because it's cool – Use the right tool for the job