Why is PostgreSQL 9.2 slower than 9.1 in my tests?

[Patryk Sidzina <patryk.sidzina@xxxxxxxxx>]

I have upgraded from PostgreSQL 9.1.5 to 9.2.1:

    "PostgreSQL 9.1.5 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4), 64-bit"

    "PostgreSQL 9.2.1 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4), 64-bit"

It is on the same machine with default PostgreSQL configuration files (only port was changed).

For testing purpose I have simple table:

    CREATE TEMP TABLE test_table_md_speed(id serial primary key, n integer);

Which I test using function:

CREATE OR REPLACE FUNCTION TEST_DB_SPEED(cnt integer) RETURNS text AS $$

DECLARE

time_start timestamp;

time_stop timestamp;

time_total interval;

BEGIN

time_start := cast(timeofday() AS TIMESTAMP);

FOR i IN 1..cnt LOOP

INSERT INTO test_table_md_speed(n) VALUES (i);

END LOOP;

time_stop := cast(timeofday() AS TIMESTAMP);

time_total := time_stop-time_start;

RETURN extract (milliseconds from time_total);

END;

$$ LANGUAGE plpgsql;

And I call:

SELECT test_db_speed(1000000);

I see strange results. For PostgreSQL 9.1.5 I get "8254.769", and for 9.2.1 I get: "9022.219". This means that new version is slower. I cannot find why.

Any ideas why those results differ?

-- 

Patryk Sidzina