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| author | Noah Misch <noah@leadboat.com> | 2013-09-25 23:09:50 -0400 |
|---|---|---|
| committer | Noah Misch <noah@leadboat.com> | 2013-09-25 23:11:34 -0400 |
| commit | c2df45a37cd9e32815fe2786cbb3ef905daaa7d2 (patch) | |
| tree | f110318cef8e588033878e3c955cd7817dd516a5 /contrib | |
| parent | 77ae7f7c356064f5355e004b95f485358dfc1360 (diff) | |
| download | postgresql-c2df45a37cd9e32815fe2786cbb3ef905daaa7d2.tar.gz | |
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
Diffstat (limited to 'contrib')
| -rw-r--r-- | contrib/pgbench/pgbench.c | 10 |
1 files 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; |