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How To Repair MySQL Replication

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Submitted by falko (Contact Author) (Forums) on Fri, 2008-06-06 12:10. :: MySQL

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How To Repair MySQL Replication

Version 1.0 Author: Falko Timme <ft [at] falkotimme [dot] com> Last edited 05/29/2008

How To Repair MySQL Replication | HowtoForge - Linux Howtos and Tutorials

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If you have set up MySQL replication, you probably know this problem: sometimes there are invalid MySQL queries which cause the replication to not work anymore. In this short guide I explain how you can repair the replication on the MySQL slave without the need to set it up from scratch again.

I do not issue any guarantee that this will work for you!

1 Identifying The ProblemTo find out whether replication is/is not working and what has caused to stop it, you can take a look at the logs. On Debian, for example, MySQL logs to /var/log/syslog:

grep mysql /var/log/syslog

server1:/home/admin# grep mysql /var/log/syslog

May 29 09:56:08 http2 mysqld[1380]: 080529 9:56:08 [ERROR] Slave: Error 'Table 'mydb.

taggregate_temp_1212047760' doesn't exist' on query. Default database: 'mydb'. Query: 'UPDATE thread AS

thread,taggregate_temp_1212047760 AS aggregate

May 29 09:56:08 http2 mysqld[1380]: ^ISET thread.views = thread.views + aggregate.views

May 29 09:56:08 http2 mysqld[1380]: ^IWHERE thread.threadid = aggregate.threadid', Error_code: 1146

May 29 09:56:08 http2 mysqld[1380]: 080529 9:56:08 [ERROR] Error running query, slave SQL thread aborted. Fix

the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.001079'

position 203015142

server1:/home/admin#

You can see what query caused the error, and at what log position the replication stopped.

To verify that the replication is really not working, log in to MySQL:

mysql -u root -p

On the MySQL shell, run:

mysql> SHOW SLAVE STATUS \G

If one of Slave_IO_Running or Slave_SQL_Running is set to No, then the replication is broken:

mysql> SHOW SLAVE STATUS \G

*************************** 1. row ***************************

Slave_IO_State: Waiting for master to send event

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Master_Host: 1.2.3.4

Master_User: slave_user

Master_Port: 3306

Connect_Retry: 60

Master_Log_File: mysql-bin.001079

Read_Master_Log_Pos: 269214454

Relay_Log_File: slave-relay.000130

Relay_Log_Pos: 100125935

Relay_Master_Log_File: mysql-bin.001079

Slave_IO_Running: Yes

Slave_SQL_Running: No

Replicate_Do_DB: mydb

Replicate_Ignore_DB:

Replicate_Do_Table:

Replicate_Ignore_Table:

Replicate_Wild_Do_Table:

Replicate_Wild_Ignore_Table:

Last_Errno: 1146

Last_Error: Error 'Table 'mydb.

taggregate_temp_1212047760' doesn't exist' on query. Default database: 'mydb'.

Query: 'UPDATE thread AS thread,taggregate_temp_1212047760 AS aggregate

SET thread.views = thread.views + aggregate.views

WHERE thread.threadid = aggregate.threadid'

Skip_Counter: 0

Exec_Master_Log_Pos: 203015142

Relay_Log_Space: 166325247

Until_Condition: None

Until_Log_File:

Until_Log_Pos: 0

Master_SSL_Allowed: No

Master_SSL_CA_File:

Master_SSL_CA_Path:

Master_SSL_Cert:

Master_SSL_Cipher:

Master_SSL_Key:

Seconds_Behind_Master: NULL

1 row in set (0.00 sec) mysql>

2 Repairing The ReplicationJust to go sure, we stop the slave:

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mysql> STOP SLAVE;

Fixing the problem is actually quite easy. We tell the slave to simply skip the invalid SQL query:

mysql> SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1;

This tells the slave to skip one query (which is the invalid one that caused the replication to stop). If you'd like to skip two queries, you'd use SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 2; instead and so on.

That's it already. Now we can start the slave again...

mysql> START SLAVE;

... and check if replication is working again:

mysql> SHOW SLAVE STATUS \G

mysql> SHOW SLAVE STATUS \G

*************************** 1. row ***************************

Slave_IO_State: Waiting for master to send event

Master_Host: 1.2.3.4

Master_User: slave_user

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Master_Port: 3306

Connect_Retry: 60

Master_Log_File: mysql-bin.001079

Read_Master_Log_Pos: 447560366

Relay_Log_File: slave-relay.000130

Relay_Log_Pos: 225644062

Relay_Master_Log_File: mysql-bin.001079

Slave_IO_Running: Yes

Slave_SQL_Running: Yes

Replicate_Do_DB: mydb

Replicate_Ignore_DB:

Replicate_Do_Table:

Replicate_Ignore_Table:

Replicate_Wild_Do_Table:

Replicate_Wild_Ignore_Table:

Last_Errno: 0

Last_Error:

Skip_Counter: 0

Exec_Master_Log_Pos: 447560366

Relay_Log_Space: 225644062

Until_Condition: None

Until_Log_File:

Until_Log_Pos: 0

Master_SSL_Allowed: No

Master_SSL_CA_File:

Master_SSL_CA_Path:

Master_SSL_Cert:

Master_SSL_Cipher:

Master_SSL_Key:

Seconds_Behind_Master: 0

1 row in set (0.00 sec) mysql>

As you see, both Slave_IO_Running and Slave_SQL_Running are set to Yes now.

Now leave the MySQL shell...

mysql> quit;

... and check the log again:

grep mysql /var/log/syslog

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How To Repair MySQL Replication | HowtoForge - Linux Howtos and Tutorials

server1:/home/admin# grep mysql /var/log/syslog

May 29 09:56:08 http2 mysqld[1380]: 080529 9:56:08 [ERROR] Slave: Error 'Table 'mydb.

taggregate_temp_1212047760' doesn't exist' on query. Default database: 'mydb'. Query: 'UPDATE thread AS

thread,taggregate_temp_1212047760 AS aggregate

May 29 09:56:08 http2 mysqld[1380]: ^ISET thread.views = thread.views + aggregate.views

May 29 09:56:08 http2 mysqld[1380]: ^IWHERE thread.threadid = aggregate.threadid', Error_code: 1146

May 29 09:56:08 http2 mysqld[1380]: 080529 9:56:08 [ERROR] Error running query, slave SQL thread aborted. Fix

the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.001079'

position 203015142

May 29 11:42:13 http2 mysqld[1380]: 080529 11:42:13 [Note] Slave SQL thread initialized, starting replication

in log 'mysql-bin.001079' at position 203015142, relay log '/var/lib/mysql/slave-relay.000130' position:

100125935

server1:/home/admin#

The last line says that replication has started again, and if you see no errors after that line, everything is ok.

3 Links

● MySQL: http://www.mysql.com

Copyright © 2008 Falko Timme

All Rights Reserved.

●

● ●

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Related Tutorials● Setting Up Master-Master Replication With MySQL 5 On Debian Etch

● Master-Master Replication With MySQL 5 On Fedora 8

● How To Set Up Database Replication In MySQL

Please do not use the comment function to ask for help! If you need help, please use our forum. Comments will be published after administrator approval.

Slave_IO_Running: No and Seconds_Behind_Master: NULLSubmitted by Ramanath (not registered) on Mon, 2011-03-14 11:13.

What i have to do if Slave_IO_Running: No and Seconds_Behind_Master: NULL. Please help me.I am waiting for your

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How To Repair MySQL Replication | HowtoForge - Linux Howtos and Tutorials

response.

http://www.howtoforge.com/how-to-repair-mysql-replication.. In this link you have mentioned the solution for Slave_SQL_Running: No.Please suggest me for Slave_IO_Running: No and Seconds_Behind_Master: NULL

reply | view as pdf

Thank you. I got replication workingSubmitted by Farshid (not registered) on Sat, 2010-10-23 23:13.

Thank you. I got replication working without having to rebuild in middle of night remotely!

reply | view as pdf

ThanksSubmitted by sureshkumar (not registered) on Fri, 2009-07-03 10:46.

Thanks.......... Good work ...

reply | view as pdf

Be careful, though...Submitted by Richard (not registered) on Thu, 2009-01-15 16:51.

Bear in mind that any time you have a query which *did* successfully execute on the master and is skipped on the slave and you use a SQL_SLAVE_SKIP_COUNTER method to "fix" the problem, your master and slave are now no longer in sync. Yes, this is sometimes necessary, but if it is a recurring issue, then the problems go much deeper than merely broken replication.

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Re: Be careful, though...Submitted by Anonymous (not registered) on Tue, 2009-11-24 07:42.

noted that this is not the proper "fix" for the problem, but we are missing your proposed solution

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Re: Be careful, though...Submitted by Anonymous (not registered) on Thu, 2009-01-29 21:20.

True, but, sometimes the slave will try to execute things that don't apply like a "drop trigger" statement for a trigger that doesn't ever exist because the slave is only replicating specific tables.

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Re: Be careful, though...Submitted by Anonymous (not registered) on Sun, 2009-01-18 01:43.

Indeed. And if you skip a query to 'fix' the replication, you run the very serious risk that the replication will become even more out of sync further down the line. This isn't fixing, it's just brushing the problem under the carpet and hoping it goes away. If you must skip a query, look at the query first, and be sure its absence won't cause future queries to fail

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Automated Script InquirySubmitted by Perry Whelan (not registered) on Wed, 2008-10-22 17:32.

I'm managing an infrastructure with a number of databases who (for codified reasons that I cannot influence) suffer from this situation often. So, I've written a cron script to manage the situation.

Does anyone see any foreseeable issues with this logic (see below)?

#!/bin/bash

## Tool to unstick MySQL Replicators.

## Set to run from cron once a minute.

# */1 * * * * /usr/local/bin/whipSlave.mysql.sh > /dev/null 2>&1

# Last updated: MM/DD/YYYY

COMMANDS="mysql grep awk logger"

export PATH='/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin'

for i in $COMMANDS

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do

X=`echo $i | tr '[a-z]' '[A-Z]'`

export $X=`type -p $i`

done

# Define variables

USERNAME=dbuser

PASSWORD=password

# Define Functions

## Obtain MwSQL slave server status

function SLAVE()

{

STATUS=`$MYSQL -u $USERNAME -p$PASSWORD -e \

"SHOW SLAVE STATUS \G" |

$GREP Seconds_Behind_Master |

$AWK '{print $2}'`

}

## Skip errors

function UNSTICK()

{

$MYSQL -u $USERNAME -p$PASSWORD -e \

"STOP SLAVE; SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; START SLAVE;"

sleep 5

# Check everything again

CHECK

}

## Decide what to do...

function CHECK()

{

# Obtain status

SLAVE

if [ $STATUS = NULL ]

then

# I think the replicator is broken

echo "MySQL Slave database is not replicating. Fixing..." | $LOGGER

UNSTICK

else

# Everything should be fine

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echo "MySQL Slave is $STATUS seconds behind its Master." | $LOGGER

fi

}

## Are we running?

function ALIVE()

{

UP=`$MYSQL -u $USERNAME -p$PASSWORD -e \

"SHOW SLAVE STATUS \G" |

$GREP Slave_IO_Running |

$AWK '{print $2}'`

if [ $UP = Yes ]

then

# Let's check if everything is good, then...

CHECK

else

# Uh oh...let's not do anything.

echo "MySQL Slave IO is not running!" | $LOGGER

exit 1

fi

}

# How is everything?

ALIVE

#EoF

exit 0

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Re: Automated Script InquirySubmitted by Jeff Buchbinder (not registered) on Thu, 2009-01-15 17:33.

This might be a little bit simpler (works with MySQL 5.0+, I believe):

#!/bin/bash done=0 while [ $done -eq 0 ]; do # get status done=$( mysql -Be 'show

slave status;' | tail -1 | cut -f12 | grep Yes | wc -l ) if [ $done -eq 0 ]; then

echo "Advancing position past [$(mysql -Be 'show slave status;' | tail -1 | cut -

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f20)]... " mysql -uroot -Be "SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; start slave;"

sleep 1 fi done

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Re: Re: Automated Script InquirySubmitted by Anonymous (not registered) on Sat, 2011-10-01 14:42.

while [ ! "`mysql -uroot -Be 'SET GLOBAL

SQL_SLAVE_SKIP_COUNTER = 1; start slave;'`" ]

do

echo "Skipped one Error"

sleep 1

done ; echo "All set"

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