How to re-sync the Mysql DB if Master and slave have different database incase of Mysql replication

Question

Mysql Server1 is running as MASTER  Mysql Server2 is running as SLAVE   Now DB replication is happening from MASTER to SLAVE   Server2 is removed from network and re-connect it back after 1 day  After this there is mismatch in database in master and slave   How to re-sync the DB again as after restoring DB taken from Master to Slave also doesn t solve the problem

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I am very late to this question  however I did encounter this problem and  after much searching  I found this information from Bryan Kennedy   http   plusbryan com mysql-replication-without-downtime  On Master take a backup like this  mysqldump --skip-lock-tables --single-transaction --flush-logs --hex-blob --master-data 2 -A      dump sql  Now  examine the head of the file and jot down the values for MASTER LOG FILE and MASTER LOG POS  You will need them later  head dump sql -n80   grep  MASTER LOG   Copy the  dump sql  file over to Slave and restore it  mysql -u mysql-user -p  lt    dump sql  Connect to Slave mysql and run a command like this  CHANGE MASTER TO MASTER HOST  master-server-ip   MASTER USER  replication-user   MASTER PASSWORD  slave-server-password   MASTER LOG FILE  value from above   MASTER LOG POS value from above  START SLAVE   To check the progress of Slave  SHOW SLAVE STATUS   If all is well  Last Error will be blank  and Slave IO State will report    Waiting for master to send event      Look for Seconds Behind Master which indicates how far behind it is   YMMV

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I think  Maatkit utilits helps for you  You can use mk-table-sync  Please see this link  http   www maatkit org doc mk-table-sync html

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sometimes you just need to give the slave a kick too  try  stop slave      reset slave      start slave      show slave status    quite often  slaves  they just get stuck guys

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Here is what I typically do when a mysql slave gets out of sync   I have looked at mk-table-sync but thought the Risks section was scary looking   On Master   SHOW MASTER STATUS   The outputted columns  File  Position  will be of use to us in a bit   On Slave   STOP SLAVE   Then dump the master db and import it to the slave db   Then run the following   CHANGE MASTER TO   MASTER LOG FILE   File      MASTER LOG POS  Position   START SLAVE    Where  File  and  Position  are the values outputted from the  SHOW MASTER STATUS  ran above   Hope this helps

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This is the full step-by-step procedure to resync a master-slave replication from scratch   At the master   RESET MASTER  FLUSH TABLES WITH READ LOCK  SHOW MASTER STATUS    And copy the values of the result of the last command somewhere   Without closing the connection to the client  because it would release the read lock  issue the command to get a dump of the master   mysqldump -u root -p --all-databases  gt   a path mysqldump sql   Now you can release the lock  even if the dump hasn t ended yet  To do it  perform the following command in the MySQL client   UNLOCK TABLES    Now copy the dump file to the slave using scp or your preferred tool   At the slave   Open a connection to mysql and type   STOP SLAVE    Load master s data dump with this console command   mysql -uroot -p  lt  mysqldump sql   Sync slave and master logs   RESET SLAVE  CHANGE MASTER TO MASTER LOG FILE  mysql-bin 000001   MASTER LOG POS 98    Where the values of the above fields are the ones you copied before   Finally  type   START SLAVE    To check that everything is working again  after typing   SHOW SLAVE STATUS    you should see   Slave IO Running  Yes Slave SQL Running  Yes   That s it

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Unless you are writing directly to the slave  Server2  the only problem should be that Server2 is missing any updates that have happened since it was disconnected   Simply restarting the slave with  START SLAVE   should get everything back up to speed

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I created a GitHub repo with an script to solve this problem quickly  Just change a couple variables and run it  First  the script creates a backup of your database    I hope this help you  and others people too    How to Reset  Re-Sync  MySQL Master-Slave Replication

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Rebuilding the slave using LVM  Here is the method we use to rebuild MySQL slaves using Linux LVM  This guarantees a consistent snapshot while requiring very minimal downtime on your master   Set innodb max dirty pages percent to zero on the master MySQL server  This will force MySQL to write all the pages to the disk which will significantly speed up the restart   set global innodb max dirty pages pct   0    To monitor the number of dirty pages run the command  mysqladmin ext -i10   grep dirty   Once the number stop decreasing you have reach the point to continue  Next reset the master to clear the old bin logs   relay logs   RESET MASTER    Execute lvdisplay to get LV Path  lvdisplay   Output will look like this  --- Logical volume --- LV Path                 dev vg mysql lv data LV Name                lv data VG Name                vg mysql   Shutdown the master database with command  service mysql stop   Next take a snaphot  mysql snapshot will be the new logical volume name  If binlogs are place on the OS drive those need to be snapshot as well   lvcreate --size 10G --snapshot --name mysql snapshot  dev vg mysql lv data   Start master again with command  service mysql start   Restore dirty pages setting to the default  set global innodb max dirty pages pct   75    Run lvdisplay again to make sure the snapshot is there and visible  lvdisplay   Output   --- Logical volume --- LV Path                 dev vg mysql mysql snapshot LV Name                mysql snapshot VG Name                vg mysql   Mount the snapshot  mkdir  mnt mysql snapshot mount  dev vg mysql mysql snapshot  mnt mysql snapshot   If you have an existing MySQL slave running you need to stop it  service mysql stop   Next you need to clear MySQL data folder  cd  var lib mysql rm -fr     Back to master  Now rsync the snapshot to the MySQL slave  rsync --progress -harz  mnt mysql snapshot  targethostname  var lib mysql    Once rsync has completed you may unmount and remove the snapshot  umount  mnt mysql snapshot lvremove -f  dev vg mysql mysql snapshot   Create replication user on the master if the old replication user doesn t exist or password is unknown  GRANT REPLICATION SLAVE on     to  replication    SLAVE IP   identified by  YourPass     Verify that  var lib mysql data files are owned by the mysql user  if so you can omit the following command   chown -R mysql mysql  var lib mysql   Next record the binlog position  ls -laF   grep mysql-bin   You will see something like     -rw-rw----     1 mysql mysql  1073750329 Aug 28 03 33 mysql-bin 000017 -rw-rw----     1 mysql mysql  1073741932 Aug 28 08 32 mysql-bin 000018 -rw-rw----     1 mysql mysql   963333441 Aug 28 15 37 mysql-bin 000019 -rw-rw----     1 mysql mysql    65657162 Aug 28 16 44 mysql-bin 000020   Here the master log file is the highest file number in sequence and bin log position is the file size  Record these values   master log file mysql-bin 000020 master log post 65657162   Next start the slave MySQL  service mysql start   Execute change master command on the slave by executing the following   CHANGE MASTER TO  master host  10 0 0 12    master user  replication    master password  YourPass    master log file  mysql-bin 000020    master log pos 65657162     Finally start the slave  SLAVE START    Check slave status   SHOW SLAVE STATUS    Make sure Slave IO is running and there are no connection errors  Good luck   BR  Juha Vehnia  I recently wrote this on my blog which is found here    There are few more details there but the story is the same   http   www juhavehnia com 2015 05 rebuilding-mysql-slave-using-linux-lvm html

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Adding to the popular answer to include this error     ERROR 1200  HY000   The server is not configured as slave  fix in config file or with CHANGE MASTER TO     Replication from slave in one shot   In one terminal window    mysql -h  lt Master IP Address gt  -uroot -p   After connecting   RESET MASTER  FLUSH TABLES WITH READ LOCK  SHOW MASTER STATUS    The status appears as below  Note that position number varies    ------------------ ---------- -------------- ------------------    File               Position   Binlog Do DB   Binlog Ignore DB    ------------------ ---------- -------------- ------------------    mysql-bin 000001        98    your DB                            ------------------ ---------- -------------- ------------------    Export the dump similar to how he described  using another terminal    Exit and connect to your own DB which is the slave    mysql -u root -p   The type the below commands   STOP SLAVE    Import the Dump as mentioned  in another terminal  of course   and type the below commands   RESET SLAVE  CHANGE MASTER TO    MASTER HOST    Master IP Address      MASTER USER    your Master user      usually the  root  user   MASTER PASSWORD    Your MasterDB Password      MASTER PORT   3306     MASTER LOG FILE    mysql-bin 000001      MASTER LOG POS   98     In this case   Once logged  set the server id parameter  usually  for new   non-replicated DBs  this is not set by default     set global server id 4000    Now  start the slave   START SLAVE  SHOW SLAVE STATUS G    The output should be the same as he described     Slave IO Running  Yes   Slave SQL Running  Yes   Note  Once replicated  the master and slave share the same password

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Here is a complete answer that will hopefully help others       I want to setup mysql replication using master and slave  and since the only thing I knew was that it uses log file s  to synchronize  if the slave goes offline and gets out of sync  in theory it should only need to connect back to its master and keep reading the log file from where it left off  as user malonso mentioned   So here are the test result after configuring the master and slave as mentioned by  http   dev mysql com doc refman 5 0 en replication-howto html      Provided you use the recommended master slave configuration and don t write to the slave  he and I where right  as far as mysql-server 5 x is concerned   I didn t even need to use  START SLAVE    it just caught up to its master  But there is a default 88000 something retries every 60 second so I guess if you exhaust that you might have to start or restart the slave  Anyways  for those like me who wanted to know if having a slave going offline and back up again requires manual intervention   no  it doesn t   Maybe the original poster had corruption in the log-file s   But most probably not just a server going off-line for a day     pulled from  usr share doc mysql-server-5 1 README Debian gz which probably makes sense to non debian servers as well     FURTHER NOTES ON REPLICATION                                 If the MySQL server is acting as a replication slave  you should not set --tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts  A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations  If files in the temporary file directory are lost when the server restarts  replication fails    you can use something sql like  show variables like  tmpdir   to find out

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The documentation for this at the MySQL site is woefully out of date and riddled with foot-guns  such as interactive timeout   Issuing FLUSH TABLES WITH READ LOCK as part of your export of the master generally only makes sense when coordinated with a storage filesystem snapshot such as LVM or zfs   If you are going to use mysqldump  you should rely instead on the --master-data option to guard against human error and release the locks on the master as quickly as possible   Assume the master is 192 168 100 50 and the slave is 192 168 100 51  each server has a distinct server-id configured  the master has binary logging on and the slave has read-only 1 in my cnf  To stage the slave to be able to start replication just after importing the dump  issue a CHANGE MASTER command but omit the log file name and position   slaveserver gt  CHANGE MASTER TO MASTER HOST  192 168 100 50   MASTER USER  replica   MASTER PASSWORD  asdmk3qwdq1     Issue the GRANT on the master for the slave to use   masterserver gt  GRANT REPLICATION SLAVE ON     TO  replica   192 168 100 51  IDENTIFIED BY  asdmk3qwdq1     Export the master  in screen  using compression and automatically capturing the correct binary log coordinates   mysqldump --master-data --all-databases --flush-privileges   gzip -1  gt  replication sql gz   Copy the replication sql gz file to the slave and then import it with zcat to the instance of MySQL running on the slave   zcat replication sql gz   mysql   Start replication by issuing the command to the slave   slaveserver gt  START SLAVE    Optionally update the  root  my cnf on the slave to store the same root password as the master   If you are on 5 1   it is best to first set the master s binlog format to MIXED or ROW  Beware that row logged events are slow for tables which lack a primary key  This is usually better than the alternative  and default  configuration of binlog format statement  on master   since it is less likely to produce the wrong data on the slave   If you must  but probably shouldn t  filter replication  do so with slave options replicate-wild-do-table dbname   or replicate-wild-ignore-table badDB   and use only binlog format row  This process will hold a global lock on the master for the duration of the mysqldump command but will not otherwise impact the master   If you are tempted to use mysqldump --master-data --all-databases --single-transaction  because you only using InnoDB tables   you are perhaps better served using MySQL Enterprise Backup or the open source implementation called xtrabackup  courtesy of Percona

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We are using master-master replication technique of MySQL and if one MySQL server say 1 is removed from the network it reconnects itself after the connection are restored and all the records that were committed in the in the server 2 which was in the network are transferred to the server 1 which has lost the connection after restoration  Slave thread in the MySQL retries to connect to its master after every 60 sec by default  This property can be changed as MySQL ha a flag  master connect retry 5  where 5 is in sec  This means that we want a retry after every 5 sec   But you need to make sure that the server which lost the connection show not make any commit in the database as you get duplicate Key error Error code  1062

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Following up on David s answer     Using SHOW SLAVE STATUS G will give human-readable output

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Master     mysqldump -u root -p --all-databases --master-data   gzip  gt   tmp dump sql gz     scp master  tmp dump sql gz slave  tmp  Move dump file to slave server  Slave     STOP SLAVE    zcat  tmp dump sql gz   mysql -u root -p  START SLAVE  SHOW SLAVE STATUS      NOTE  On master you can run SET GLOBAL expire logs days   3 to keep binlogs for 3 days in case of slave issues

[mysql] How to re-sync the Mysql DB if Master and slave have different database incase of Mysql replication?

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