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16.7.9.1. Automating Synchronization of the Slave to the Master binlog

It is possible to automate much of the process described in the previous section (see Section 16.7.9, “MySQL Cluster Backups With Replication”). The following Perl script reset-slave.pl serves as an example of how you can do this.

#!/user/bin/perl -w

#  file: reset-slave.pl

#  Copyright ©2005 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; either version 2 of the License, or
#  (at your option) any later version.

#  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: 
#  Free Software Foundation, Inc. 
#  59 Temple Place, Suite 330 
#  Boston, MA 02111-1307 USA
#
#  Version 1.1


######################## Includes ###############################

use DBI;

######################## Globals ################################

my  $m_host='';
my  $m_port='';
my  $m_user='';
my  $m_pass='';
my  $s_host='';
my  $s_port='';
my  $s_user='';
my  $s_pass='';
my  $dbhM='';
my  $dbhS='';

####################### Sub Prototypes ##########################

sub CollectCommandPromptInfo;
sub ConnectToDatabases;
sub DisconnectFromDatabases;
sub GetSlaveEpoch;
sub GetMasterInfo;
sub UpdateSlave;

######################## Program Main ###########################

CollectCommandPromptInfo;
ConnectToDatabases;
GetSlaveEpoch;
GetMasterInfo;
UpdateSlave;
DisconnectFromDatabases;

################## Collect Command Prompt Info ##################

sub CollectCommandPromptInfo
{
  ### Check that user has supplied correct number of command line args
  die "Usage:\n
       reset-slave >master MySQL host< >master MySQL port< \n
                   >master user< >master pass< >slave MySQL host< \n
                   >slave MySQL port< >slave user< >slave pass< \n
       All 8 arguments must be passed. Use BLANK for NULL passwords\n"
       unless @ARGV == 8;

  $m_host  =  $ARGV[0];
  $m_port  =  $ARGV[1];
  $m_user  =  $ARGV[2];
  $m_pass  =  $ARGV[3];
  $s_host  =  $ARGV[4];
  $s_port  =  $ARGV[5];
  $s_user  =  $ARGV[6];
  $s_pass  =  $ARGV[7];

  if ($m_pass eq "BLANK") { $m_pass = '';}
  if ($s_pass eq "BLANK") { $s_pass = '';}
}

###############  Make connections to both databases #############

sub ConnectToDatabases
{
  ### Connect to both master and slave cluster databases

  ### Connect to master
  $dbhM
    = DBI->connect(
    "dbi:mysql:database=cluster_replication;host=$m_host;port=$m_port",
    "$m_user", "$m_pass")
      or die "Can't connect to Master Cluster MySQL process!
              Error: $DBI::errstr\n";

  ### Connect to slave
  $dbhS 
    = DBI->connect(
          "dbi:mysql:database=cluster_replication;host=$s_host",
          "$s_user", "$s_pass")
    or die "Can't connect to Slave Cluster MySQL process!
            Error: $DBI::errstr\n";
}

################  Disconnect from both databases ################

sub DisconnectFromDatabases
{
  ### Disconnect from master

  $dbhM->disconnect
  or warn " Disconnection failed: $DBI::errstr\n";

  ### Disconnect from slave

  $dbhS->disconnect
  or warn " Disconnection failed: $DBI::errstr\n";
}

######################  Find the last good GCI ##################

sub GetSlaveEpoch
{
  $sth = $dbhS->prepare("SELECT MAX(epoch)
                         FROM cluster_replication.apply_status;")
      or die "Error while preparing to select epoch from slave: ", 
             $dbhS->errstr;

  $sth->execute
      or die "Selecting epoch from slave error: ", $sth->errstr;

  $sth->bind_col (1, \$epoch);
  $sth->fetch;
  print "\tSlave Epoch =  $epoch\n";
  $sth->finish;
}

#######  Find the position of the last GCI in the binlog ########

sub GetMasterInfo
{
  $sth = $dbhM->prepare("SELECT 
                           SUBSTRING_INDEX(File, '/', -1), Position
                         FROM cluster_replication.binlog_index
                         WHERE epoch > $epoch 
                         ORDER BY epoch ASC LIMIT 1;")
      or die "Prepare to select from master error: ", $dbhM->errstr;

  $sth->execute
      or die "Selecting from master error: ", $sth->errstr;

  $sth->bind_col (1, \$binlog);
  $sth->bind_col (2, \$binpos);
  $sth->fetch;
  print "\tMaster bin log =  $binlog\n";
  print "\tMaster Bin Log position =  $binpos\n";
  $sth->finish;
}

##########  Set the slave to process from that location #########

sub UpdateSlave
{
  $sth = $dbhS->prepare("CHANGE MASTER TO
                         MASTER_LOG_FILE='$binlog',
                         MASTER_LOG_POS=$binpos;")
      or die "Prepare to CHANGE MASTER error: ", $dbhS->errstr;

  $sth->execute
       or die "CHNAGE MASTER on slave error: ", $sth->errstr;
  $sth->finish;
  print "\tSlave has been updated. You may now start the slave.\n";
}

# end reset-slave.pl

 
 
  Published under the terms of the GNU General Public License Design by Interspire