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Fix pgbench's getrand() function so that min and max have approximately

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the same chance of being selected as do numbers between them.  Problem
noted by Greg Stark; fix by Alexey Klyukin.
This commit is contained in:
Tom Lane 2008-03-10 01:23:04 +00:00
parent d9384a4b73
commit 9537739f7f
1 changed files with 7 additions and 3 deletions
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10
contrib/pgbench/pgbench.c
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@ -1,5 +1,5 @@
/* /*
* $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.75 2007/12/11 02:31:49 tgl Exp $ * $PostgreSQL: pgsql/contrib/pgbench/pgbench.c,v 1.76 2008/03/10 01:23:04 tgl Exp $
* *
* pgbench: a simple benchmark program for PostgreSQL * pgbench: a simple benchmark program for PostgreSQL
* written by Tatsuo Ishii * written by Tatsuo Ishii
@ -191,11 +191,15 @@ usage(void)
fprintf(stderr, "(initialize mode): pgbench -i [-h hostname][-p port][-s scaling_factor] [-F fillfactor] [-U login][-d][dbname]\n"); fprintf(stderr, "(initialize mode): pgbench -i [-h hostname][-p port][-s scaling_factor] [-F fillfactor] [-U login][-d][dbname]\n");
} }
/* random number generator */ /* random number generator: uniform distribution from min to max inclusive */
static int static int
getrand(int min, int max) getrand(int min, int max)
{ {
return min + (int) (((max - min) * (double) random()) / MAX_RANDOM_VALUE + 0.5); /*
* Odd coding is so that min and max have approximately the same chance of
* being selected as do numbers between them.
*/
return min + (int) (((max - min + 1) * (double) random()) / (MAX_RANDOM_VALUE + 1.0));
} }
/* call PQexec() and exit() on failure */ /* call PQexec() and exit() on failure */