Administrations

MySQL Master-Master or Master-Slave Replication Error Fix

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Scenario Master – Master replication

MasterA is a client facing server
MasterB is a warm standby server (read only)

MasterB restarted abruptly and when instances were braught back up MasterA (it’s slave) was showing the following error:

MasterA has the following error in show slave status:

Last_IO_Errno: 1236
Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: ‘Could not find first log file name in binary log index file’

Solution:

Slave: stop slave;

Master: flush logs

Master: show master status; — take note of the master log file and master log position

Slave: CHANGE MASTER TO MASTER_LOG_FILE=’log-bin.00000X′, MASTER_LOG_POS=106;

Slave: start slave;

Read more: http://mysqlpreacher.com/wordpress/2010/12/could-not-find-first-log-file-name-in-binary-log-index-file/#ixzz2ILRnl4XI

Src: http://mysqlpreacher.com/wordpress/2010/12/could-not-find-first-log-file-name-in-binary-log-index-file/

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Enabling munin node plug-ins on Debian

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Munin uses plug-ins to determine what data is gathered and reported. It includes several plug-ins for the types of data most people would be interested in, but not all of those plug-ins are enabled on a fresh installation.
What are plug-ins?

When a munin node gathers data about a slice so it can be graphed, the node reads instructions from files called "plug-ins" to determine what information to collect. Several plug-ins are installed with munin but not all of them are used by default. Fortunately a munin node installation includes a command that lets you see what plug-ins are active and can help you decide which others to enable.

The munin-node-configure command

The "munin-node-configure" command can list the status of installed munin plug-ins, suggest which to enable, and provide a shell script that will automate enabling the appropriate plug-ins. Using this command isn't the only way to perform these tasks, but it's convenient and easy to use. Easy is good.

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Monitor MySQL database restore progress with pv

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The pv command is one that I really enjoy using but it's also one that I often forget about. You can't get a much more concise definition of what pv does than this one:

pv allows a user to see the progress of data through a pipeline, by giving information such as time elapsed, percentage completed (with progress bar), current throughput rate, total data transferred, and ETA.

The usage certainly isn't complicated:

To use it, insert it in a pipeline between two processes, with the appropriate options. Its standard input will be passed through to its standard output and progress will be shown on standard error.

A great application of pv is when you're restoring large amounts of data into MySQL, especially if you're restoring data under duress due to an accidentally-dropped table or database. (Who hasn't been there before?) The standard way of restoring data is something we're all familiar with:

# mysql my_database < database_backup.sql

The downside of this method is that you have no idea how quickly your restore is working or when it might be done. You could always open another terminal to monitor the tables and databases as they're created, but that can be hard to follow.

Toss in pv and that problem is solved:

# pv database_backup.sql | mysql my_database
96.8MB 0:00:17 [5.51MB/s] [==> ] 11% ETA 0:02:10

When it comes to MySQL, your restore rate is going to be different based on some different factors, so the ETA might not be entirely accurate.

Src: http://rackerhacker.com/2010/11/24/monitor-mysql-restore-progress-with-pv/

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Installing XHProf on Debian

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xhprof provides profiling information, down to the function call. This includes execution time, CPU and memory usage for each operation. The module allows you to find and optimise bottlenecks in your application. The library includes a GUI output, you just use the classes provided to create the reports.

I installed using PECL on a Debian Squeeze development server, and the first things you need are php5-dev and make;

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MySQLTuner adjust your MySQL database

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MySQLTuner is a script written in Perl that will assist you with your MySQL configuration and make recommendations for increased performance and stability. Within seconds, it will display statistics about your MySQL installation and the areas where it can be improved.

It's key to remember that MySQLTuner is a script which can assist you with your server, but it is not the solution to a badly performing MySQL server. The best performance gains come from a thorough review of the queries sent to the server, and an evaluation of the MySQL server itself. A qualified developer in your application's programming or scripting language should be able to work with a MySQL database administrator to find improvements for your server. Once the server and application are optimized well, you may need to consider hardware upgrades to the physical server itself.
This is a really useful tool for helping to optimize MySQL performance.Understanding the various my.cnf variables and how they affect performance can seem really complicated but this tool takes some of the pain away and makes it easier to understand the effects of each variable.It is especially useful to be able to see the global memory usage, memory usage per thread and the maximum possible memory usage — that is really valuable information that is otherwise complex to calculate.

Run MySQLTuner in Debian

Copy and past the below code and save it as mysqltuner.pl using nano 😉

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Adjust Apache ServerLimit and MaxClient

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MaxClients actually tells the apache to allow this many concurrent clients.

Normally this limit is at 150. You can change this limit by editing your httpd.conf file.

httpd.conf is normally located at /etc/httpd/conf/httpd.conf

nano /etc/httpd/conf/httpd.conf

ServerLimit directive to let the value of MaxClients above 256 work.
By deafult ServerLimit is 256 (and is usually not already there in httpd.conf). If it is in your httpd.conf increase it above 256 or if it is not there add it in your httpd.conf

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Monitoring multiple server using Munin on Debian/Ubuntu Distribution

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This tutorial was written for Debian Etch, but the configuration should apply to other distributions with little changes as well.

I want to say first that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!

 

1 Preliminary Note

Our munin server's hostname is server1.example.com (IP address: 192.168.0.100), and we have a web site www.example.com on it with the document root /var/www/www.example.com/web on it.

I'm using one munin client here, server2.example.com (IP address: 192.168.0.101). Of course, you can add as many client systems as you like.

 

2 Install And Configure munin On The Server

munin server (server1.example.com):

To install the munin client and server on Debian Etch, we do this:

apt-get install munin munin-node

Next, we must edit the munin configuration file /etc/munin/munin.conf. We want munin to put its output into the directory

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