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MySQL MHA and Perl pathing

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I am certainly not a knowledgeable Perl person, however I recently ran into the error Can’t locate MHA/MasterMonitor.pm on Red Hat 6.x. I have installed MySQL MHA on various systems before without any issues.

$ masterha_manager -version
Can't locate MHA/MasterMonitor.pm in @INC (@INC contains: /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at /usr/bin/masterha_manager line 26.
BEGIN failed--compilation aborted at /usr/bin/masterha_manager line 26.

The issue was that MySQL MHA is not installed in any of the acceptable default paths for this disto default installation.

$ find / -type d -name MHA
/usr/lib/perl5/vendor_perl/MHA

The fix was simple on this OS, but I expect there is a correct Perl approach?

ln -s /usr/lib/perl5/vendor_perl/MHA /usr/lib64/perl5/vendor_perl/

$ cat /etc/*release
Red Hat Enterprise Linux Server release 6.3 (Santiago)
Red Hat Enterprise Linux Server release 6.3 (Santiago)

Not a cool new feature for Master_Host

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I was surprised to find on a customer MySQL server this new syntax for Master_host in SHOW SLAVE STATUS.

mysql> SHOW SLAVE STATUSG
*************************** 1. row ***************************
               Slave_IO_State: Connecting to master
                  Master_Host: testdb1.xxx.com or 10.XXX.XX.XXX
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: db1-354215-bin-log.000005
          Read_Master_Log_Pos: 1624
               Relay_Log_File: db2-354214-relay-log.000001

Is this a fancy new Percona Server feature? No. It’s operator error.

We read a little further to find.

mysql> SHOW SLAVE STATUSG
...
             Slave_IO_Running: Connecting

...
                Last_IO_Errno: 2005
                Last_IO_Error: error connecting to master 'repl@ testdb1.xxx.com or 10.XXX.XX.XXX' - retry-time: 60  retries: 86400

How can this be created.
Using MySQL MHA, you get the following message in the output of commands to manage replication.

...
Thu Jan  3 17:06:40 2013 - [info]  All other slaves should start replication from here.
Statement should be: CHANGE MASTER TO MASTER_HOST='testdb1.xxx.com or 10.XXX.XX.XXX', MASTER_PORT=3306,
 MASTER_LOG_FILE='db1-354215-bin-log.000005', MASTER_LOG_POS=1624, MASTER_USER='repl',
MASTER_PASSWORD='xxx';
...

Needless to say, this syntax was taken literately, and MySQL did not complain.

I would suggest here that while MySQL does not do any validation on the value of the MASTER_HOST value in the CHANGE MASTER TO command to ensure it is resolvable it should at least do some validation to ensure the value is either a DNS entry or an IPV4,IPV6 value, that is space ‘ ‘, is not a valid character in these situations.

Installing MySQL MHA with Percona Server

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MySQL MHA by Oracle ACE Director Yoshinori Matsunobu is an excellent open source tool to help in providing HA with native MySQL replication. The installation however is dependent on some Perl packages and to the untrained eye this may be an issue if you are using Percona Server as your choice of MySQL implementation.

The MHA Node page requires the perl-DBD-MySQL package to be installed. The installation on RedHat/CentOS/Oracle Linux look like this:

$ sudo yum install perl-DBD-MySQL
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.anl.gov
* extras: mirror.anl.gov
* updates: mirror.anl.gov
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package perl-DBD-MySQL.x86_64 0:3.0007-2.el5 set to be updated
--> Finished Dependency Resolution

However, recently with a client the following error “mysql conflicts with Percona-Server” occurred.

$ sudo yum install perl-DBD-MySQL
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.anl.gov
* extras: mirror.anl.gov
* updates: mirror.anl.gov
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package perl-DBD-MySQL.x86_64 0:3.0007-2.el5 set to be updated
--> Processing Dependency: libmysqlclient.so.15(libmysqlclient_15)(64bit) for package: perl-DBD-MySQL
--> Processing Dependency: libmysqlclient.so.15()(64bit) for package: perl-DBD-MySQL
--> Running transaction check
---> Package mysql.x86_64 0:5.0.95-1.el5_7.1 set to be updated
--> Processing Conflict: mysql conflicts MySQL
--> Finished Dependency Resolution
mysql-5.0.95-1.el5_7.1.x86_64 from updates has depsolving problems
 --> mysql conflicts with Percona-Server-client-55
Error: mysql conflicts with Percona-Server-client-55

This is actually an easy problem to solve, but if you are unfamiliar with all the various MySQL packages for RPM’s, and you installed Percona Server with the standard documented commands you may get lost. What is necessary is the installation of the compatibility libraries, as simple as:

$ sudo yum install -y Percona-Server-shared-compat