Why does log temp files are created twice when query is executed in PL/pgSQL function? Would you please explain it to me?
PL/pgSQL materialize result internally.
Usually PostgreSQL operations are executed row by row. But some SRF functions like PLpgSQL functions doesn't support this mode, and returns tuplestore - materialized result.
Using this technique is comfortable, but with some performance risks. Unfortunately, you cannot to change this behave. Not in PL/pgSQL.
You can write C function with same functionality but with row by row returning result mode. It is not possible in PL/pgSQL.
On other hand - you can try to increase work_mem (if your server has enough RAM). Materialization are done when available memory (controlled by work_mem) is too less.
You can try
SET work_mem to '20MB';
SELECT test_tempfiles();
Regards
Pavel
As below test result. Log temp files are created twice when SELECT statement is put into a PL/pgSQL function. It led a little of performance degradation. Is there any way to define PL/pgSQL function to avoid this issue? # I am using PostgreSQL 9.3.9
my test results ----- [postgres@test]$ psql -c "select test_tempfiles();" > /dev/null LOG: temporary file: path "base/pgsql_tmp/pgsql_tmp2223.0", size 3244032 CONTEXT: PL/pgSQL function test_cursor() line 3 at RETURN QUERY LOG: temporary file: path "base/pgsql_tmp/pgsql_tmp23223.1", size 2828062 LOG: duration: 421.426 ms statement: select test_tempfiles();
[postgres@test]$ psql -c "select name from testtbl order by id" > /dev/null LOG: temporary file: path "base/pgsql_tmp/pgsql_tmp25586.0", size 2850816 LOG: duration: 389.054 ms statement: select random from testtbl order by random -----
test_tempfiles() function is defined as below ----- CREATE OR REPLACE FUNCTION public.test_tempfiles() RETURNS TABLE(name text) LANGUAGE plpgsql AS $function$ begin return query execute "select name from testtbl order by id "; end; $function$ -----