From c2df45a37cd9e32815fe2786cbb3ef905daaa7d2 Mon Sep 17 00:00:00 2001 From: Noah Misch <noah@leadboat.com> Date: Wed, 25 Sep 2013 23:09:50 -0400 Subject: [PATCH] pgbench: Correct for bias in --rate schedule generation. Previous code gave a mean delay 0.44% below target. This change also has the effect of increasing the maximum possible delay. Fabien COELHO --- contrib/pgbench/pgbench.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c index 06dd7093fa..66ae48e4a7 100644 --- a/contrib/pgbench/pgbench.c +++ b/contrib/pgbench/pgbench.c @@ -929,13 +929,17 @@ top: * that the series of delays will approximate a Poisson distribution * centered on the throttle_delay time. * - * 1000 implies a 6.9 (-log(1/1000)) to 0.0 (log 1.0) delay multiplier. + * 10000 implies a 9.2 (-log(1/10000)) to 0.0 (log 1) delay multiplier, + * and results in a 0.055 % target underestimation bias: + * + * SELECT 1.0/AVG(-LN(i/10000.0)) FROM generate_series(1,10000) AS i; + * = 1.000552717032611116335474 * * If transactions are too slow or a given wait is shorter than * a transaction, the next transaction will start right away. */ - int64 wait = (int64) - throttle_delay * -log(getrand(thread, 1, 1000)/1000.0); + int64 wait = (int64) (throttle_delay * + 1.00055271703 * -log(getrand(thread, 1, 10000)/10000.0)); thread->throttle_trigger += wait;