From: | "s anwar" <sanwar(at)gmail(dot)com> |
---|---|
To: | pgsql-novice(at)postgresql(dot)org |
Subject: | Performance of plpgsql functions |
Date: | 2006-03-16 19:41:12 |
Message-ID: | 3e3c86f90603161141q40153dabn18da2ebda6c516dd@mail.gmail.com |
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Lists: | pgsql-novice |
The following represents a simplified version of my database setup:
=============== BEGIN ================
create table A(
id int not null,
scale smallint,
val smallint[]
);
create view V as select id,q15(val,scale) as data from V;
create or replace function q15(vals smallint[], exponent smallint)
returns real[]
as '
declare
low int;
high int;
count int;
new_array real[];
multiplier real;
begin
if vals is null or exponent is null
then
return null;
end if;
multiplier := 2^(exponent-15);
low := array_lower(vals,1);
high := array_upper(vals,1);
for i in low..high loop
new_array[i] := vals[i] * multiplier;
end loop;
return new_array;
end;
' language plpgsql immutable returns null on null input;
================ END ===============
I am running Postgres 8.1.2 on dual AMD x86_64 with 2G of shared memory.
Each time I issue: select data[10] from V where id>=5000 and id<=10000;
my database server takes up 100% of one of my two processors to compute the
results. I was hoping that the "immutable" keyword would tell the database
server to cache the results as much as possible, but I don't see its
physical manifestation as yet. I am wondering if I was doing something in my
function that is the main cause of the CPU utilization.
Expanding the data is not a good option, since it will increase my database
foot-print substantially since I have multiple fields which are stored the
same way as "V.data" above. I've thought about creating a C-function to
replace my plpgsql function, but don't know how useful would that be.
Thanks.
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