#!/bin/bash
# autopurgebinlog.sh
# script to purge mysql replication log-bin
# by am3n.net
# License GNU/GPL 

# number of days to keep logbin
AGE=5 # days
AGE_MINS=$[ $AGE * 60 * 24 ]

#find mysql binary log which older than $AGE_MINS
OLDLOGS=`find /var/lib/mysql/$HOSTNAME-bin.??? -cmin +$AGE_MINS | tail -n 1 | gawk -F'/' '{print $5}'`

# change mysqluser and mysqlpass with user that have priviled to purge binary log (i.e. root)
mysql -u mysqluser -pmysqlpass mysql -e "PURGE MASTER LOGS TO '$OLDLOGS'"

Put the script on crontab, run it once a month.

crontab -e
1 1 1 * * /root/autopurgebinlog.sh

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To check replication status when I in the console and playing with replication configuration or when I have nothing to do yet I want to see a black screen

monitorreplication.sh

#!/bin/bash
while [ 1 ]
do
        # Your code goes here
        echo ""
        date
        echo "=============================="
        mysql -u backup -pmysqlback -e "show slave status\G;"

        # Modify sleep time (in seconds) as needed below
        sleep 10
done

Another scripts to send replication status via email
This script is for sending email to my dept. just incase replication stop. And I have manually delete file /root/backup/slave_problem.txt if problem solved.

checkreplication.sh

#!/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

###check if already notified###
###you have to manually delete the file after resolve the problem
if [ -f /root/backup/slave_problem.txt ]; then
exit 1;
fi

###Check if slave running###
(
echo "show slave status \G;"
) | mysql -u backup -pmysqlback 2>&1 | grep "Slave_IO_Running: No"
if [ "$?" -ne "1" ]; then
SUBJECT="DB23 - Replication IO failed"
mysql -u backup -pmysqlback -e "show slave status \G;" > /root/backup/slave_problem.txt

else

(
echo "show slave status \G;"
) | mysql -u backup -pmysqlback 2>&1 | grep "Slave_SQL_Running: No"
if [ "$?" -ne "1" ]; then
SUBJECT="DB23 - Replication SQL failed"
mysql -u backup -pmysqlback -e "show slave status \G;" > /root/backup/slave_problem.txt
fi

fi

###Send notification if replication down###
if [ -f /root/backup/slave_problem.txt ]; then
mail -s "$SUBJECT" it@myholding.com < /root/backup/slave_problem.txt
fi

This script is just to send replication status to my email only so I can monitor it if it stops, or has an error, etc.

slave_report.sh

/root/backup/slave_report.sh
#!/bin/sh
mysql -u backup -pmysqlbackup -e "show slave status \G;" > /root/backup/slave_report.txt
mail -s "Replication report on DB23" amin@rpxholding.com < /root/backup/slave_report.txt

Added the last 2 scripts into crontab:

#check replication
1,11,21,31,41,51 1-23 * * * /root/backup/checkreplication.sh > /dev/null 2>&1
5 2,6,10,14,18,22 * * * /root/backup/slave_report.sh > /dev/null 2>&1

Ref:
http://blog.taragana.com/index.php/archive/how-to-write-infinite-loop-in-bash/
http://howtoforge.com/script-to-check-if-mysql-master-master-replication-is-working-correctly

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Could not parse relay log event entry. The possible reasons are: the master’s binary log is corrupted (you can check this by running ‘mysqlbinlog’ on the binary log), the slave’s relay log is corrupted (you can check this by running ‘mysqlbinlog’ on the relay log), a network problem, or a bug in the master’s or slave’s MySQL code. If you want to check the master’s binary log or slave’s relay log, you will be able to know their names by issuing ‘SHOW SLAVE STATUS’ on this slave.

Googling up and check several paramters:

on master server:

mysql> show master status\G;
*************************** 1. row ***************************
File: replication.011
Position: 130848689
Binlog_do_db:
Binlog_ignore_db:
1 row in set (0.00 sec)

on slave server:

mysql> show slave status\G;
*************************** 1. row ***************************
Master_Host: 10.10.105.11
Master_User: repl
Master_Port: 3306
Connect_retry: 60
Master_Log_File: replication.011
Read_Master_Log_Pos: 91831752
Relay_Log_File: dragon-relay-bin.183
Relay_Log_Pos: 3551175
Relay_Master_Log_File: replication.011
Slave_IO_Running: No
Slave_SQL_Running: No
Replicate_do_db:
Replicate_ignore_db:
Last_errno: 0
Last_error: Could not parse relay log event entry. The possible
reasons are: the master's binary log is corrupted (you can check
this by running 'mysqlbinlog' on the binary log), the slave's
relay log is corrupted (you can check this by running 'mysqlbinlog'
 on the relay log), a network problem, or a bug in the master's or
slave's MySQL code. If you want to check the master's binary log or
slave's relay log, you will be able to know their names by issuing
'SHOW SLAVE STATUS' on this slave.
Skip_counter: 0
Exec_master_log_pos: 74359528
Relay_log_space: 21023399

[root@dragon mysql]# tail -f dragon.rpxholding.com.err
081129  0:54:24 Error in Log_event::read_log_event(): 'read error',
 data_len: 148, event_type: 2 081129  0:54:24 Error reading relay
log event: slave SQL thread aborted because of I/O error 081129 0:54:24
Slave: Could not parse relay log event entry. The possible reasons are:
the master's binary log is corrupted (you can check this by running
'mysqlbinlog' on the binary log),  the slave's relay log is corrupted
(you can check this by running 'mysqlbinlog' on the relay log), a network
problem, or a bug in the master's or slave's MySQL code. If you want to
check the master's binary log or slave's relay log, you will be able to
know their names by issuing 'SHOW SLAVE STATUS' on this slave. Error_code: 0

Slave IO and SQL are not running. What caused the problem  ? binlog file at master is not corrupted. That’s great and very good news. But relay log file at slave is corrupted. That’s what make replication can’t read it. Fixing the problem:

on slave server:

mysql> change master to master_log_file='replication.011',master_log_pos=74359676;
mysql> slave start;
mysql> show slave status\G;
*************************** 1. row ***************************
Master_Host: 10.10.105.11
Master_User: repl
Master_Port: 3306
Connect_retry: 60
Master_Log_File: replication.011
Read_Master_Log_Pos: 135111081
Relay_Log_File: dragon-relay-bin.001
Relay_Log_Pos: 3204826
Relay_Master_Log_File: replication.011
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_do_db:
Replicate_ignore_db:
Last_errno: 0
Last_error:
Skip_counter: 0
Exec_master_log_pos: 77564456
Relay_log_space: 60751451
1 row in set (0.00 sec)

ERROR:
No query specified

Where do I get parameter master_log_file=’replication.011′ and master_log_pos=74359676 ? it’s from “show slave status” command

• master_log_file=’replication.011′ is the last time slave read master log file and fortunately master still logging to that file too (it’s from s)
• master_log_pos=74359676 is the next log pos slave should execute a query from master. it’s from Exec_master_log_pos=74359528. So how do I know the next pos of 74359528 is 74359676? Simple! I do this:

  # cd /var/lib/mysql
  # mysqlbinlog replication.011 > replication.011.txt
  # vi replication.011.txt -- search for 74359528 and the next pos is 74359676

Next question: What caused relay log file corrupted? (only my assumption) at the time replication stop slave server also doing a full backup and transferring a 3.5GB backup file to another server. this may cause NIC at full throttle and make relay log corrupt.

PS: I still don’t what to do if my master binlog files is corrupt. Perhaps I’ll be doing a full database mirroring (copying all databases files from master to slave when mysql down just to make both servers have the same database) to make sure data integrity

References:

• http://sql.dzone.com/news/troubleshooting-relay-log-corr
• http://www.pythian.com/blogs/876/when-show-slave-status-and-the-error-log-disagree
• http://www.mysqlperformanceblog.com/2008/07/07/how-show-slave-status-relates-to-change-master-to/
• http://www.brandonchecketts.com/archives/fixing-a-corrupt-mysql-relay-log

Edit: Feb 14, 2009

The replication stop again slave server. this time after thorough investigation, found out the server is nearly at full capation (especially the /var partition). Clean some stuffs, and I get 16GB of free space. Free space indeed an important thing I should check first

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Note: Make sure you know what cause a duplicate error and does it really not important so that you can skip inserting that query.

[mysqld]
...
slave-skip-errors=1062

You can use other error code, if that error happen. Again: Make sure you know what cause the error, and why you want to skip it.
References:

• http://dev.mysql.com/doc/refman/5.0/en/replication-options-slave.html
• http://dev.mysql.com/doc/refman/5.0/en/error-messages-server.html

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