mariadb/storage/ndb/include/util/ndb_rand.h

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[PATCH] BUG#30379 Better randomise time before retry in timeout check (DBTC) timoOutLoopStartLab() checks if any transactions have been delayed for so long that we are forced to perform some action (e.g. abort, resend etc). It is *MEANT* to (according to the comment): > To avoid aborting both transactions in a deadlock detected by time-out > we insert a random extra time-out of upto 630 ms by using the lowest > six bits of the api connect reference. > We spread it out from 0 to 630 ms if base time-out is larger than 3 sec, > we spread it out from 0 to 70 ms if base time-out is smaller than 300 msec, > and otherwise we spread it out 310 ms. The comment (as all do) lies. the API connect reference is not very random, producing incredibly predictable "random" numbers. This could lead to both txns being aborted instead of just one. Before: timeout value: 123 3 timeout value: 122 2 timeout value: 122 2 timeout value: 122 2 timeout value: 123 3 After: timeout value: 127 7 timeout value: 126 6 timeout value: 129 9 timeout value: 139 19 timeout value: 137 17 timeout value: 151 31 timeout value: 130 10 timeout value: 132 12 Index: ndb-work/ndb/src/kernel/blocks/dbtc/DbtcMain.cpp =================================================================== ndb/src/common/util/Makefile.am: BUG#30379 Better randomise time before retry in timeout check (DBTC) ndb/include/util/ndb_rand.h: BUG#30379 Better randomise time before retry in timeout check (DBTC) ndb/src/common/util/ndb_rand.c: BUG#30379 Better randomise time before retry in timeout check (DBTC) ndb/src/kernel/blocks/dbtc/DbtcMain.cpp: BUG#30379 Better randomise time before retry in timeout check (DBTC)
2007-09-25 12:01:23 +02:00
/* Copyright (C) 2003 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
#ifndef NDB_RAND_H
#define NDB_RAND_H
#define NDB_RAND_MAX 32767
#ifdef __cplusplus
extern "C" {
#endif
int ndb_rand(void);
void ndb_srand(unsigned seed);
#ifdef __cplusplus
}
#endif
#endif