Replicate tables from different database of same mysql server

Question

I have one server with 2 databases, and i want to replicate several tables from one database to another. Purpose is that we uses same user's table that used in projects.

As in anothers tables used InnoDB with foreign keys to users table i've chosen a replication way.

For that I made the changes for my.cnf

master-user=root

server-id                       = 2
replicate-rewrite-db            = dou->jobs
replicate-do-table              = jobs.auth\_user
replicate-wild-do-table         = jobs.geo\_%
replicate-do-table              = jobs.user\_profile
replicate-same-server-id        = 1
report-host                     = master-is-slave

binlog-do-db                    = dou

log-bin

after syncing tables from binlog-do-db and starting slave error.log next lines appears:

111112 15:10:22 [Note] 'CHANGE MASTER TO executed'. Previous state master_host='localhost', master_port='3306', master_log_file='', master_log_pos='4'. New state master_host='localhost', master_port='3306', master_log_file='mysql-bin.000074', master_log_pos='106'.
111112 15:10:36 [Note] Slave SQL thread initialized, starting replication in log 'mysql-bin.000074' at position 106, relay log '/var/log/mysql/dell-relay-bin.000001' position: 4
111112 15:10:36 [Note] Slave I/O thread: connected to master 'root@localhost:3306',replication started in log 'mysql-bin.000074' at position 106

Seems that on this step everything is ok, and show slave status shows no errors.

mysql> show slave status\G;
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: localhost
                  Master_User: root
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000074
          Read_Master_Log_Pos: 814
               Relay_Log_File: dell-relay-bin.000002
                Relay_Log_Pos: 959
        Relay_Master_Log_File: mysql-bin.000074
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: jobs.user\_profile,jobs.auth\_user
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: jobs.geo\_%
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 814
              Relay_Log_Space: 1113
              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
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
1 row in set (0.00 sec)

ERROR: 
No query specified

The thing is that master changes does not affect slave but slave status changes.

Thanks for any help in solve that problem.

Answer 1

Out of interest would a view do what you want?

I really don't think running replication on the same instance of mysql into to the same instance is a good idea.

The other option you might want to investigate if server hardware is a problem, would to run multiple instances of mysql running off different ports on the same machine, which might help you achieve what you are looking for. This is something i am using in a test environment for simulated master DB failure and slave DB promotion.

Answer 2

I won't tell you that replicating table to the same DB is bad idea, cause of several times increased IO.

Slave is not updated, because server-id is the same for both master and slave. Usually slave ignores updates with the same server-id as it's own.

Add replicate-same-server-id to my.cnf. replicate-same-server-id documentation

Answer 3

There is many situations on where you can achive more optimisations for example. DB1 replicates to DB2 (same server). From where DB2 only has data stored for as long as 1 week. all data that is older than 1 weeks gets deleted (On db2). in such a setup for example a high traffic db server where u need it to be as clean as possible a dual db setup on the same server uses "less" resources from the server if what your server do most of the time is read data from the database. I have such a setup buth i use 4 diferent servers. server 1) 3 days. server 2) 30 days. server 3) 2 months, and server 4 all data from start. (Server 4 mostly used for gething very old registers not so much used. Sorry for my english buth i think i made a point on where you CAN and should use db replication on the same server to reduce memmory usage and cpu usage.