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MySQL 5.0 Reference Manual :: 16 MySQL Load Balancer :: 16.5 MySQL Load Balancer FAQ
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16.5. MySQL Load Balancer FAQ

Important

For more information on MySQL Load Balancer, including how to be included in the beta programme, contact .

The following section includes some common questions and answers for MySQL Load Balancer:

Questions

  • 17.5.1: The current description says that the load balancer is for read-only operation. Does that mean that MySQL Load Balancer will not accept update statements for the slaves?

  • 17.5.2: The MSQL Load Balancer is listed as being 'slave state aware'. Do you check the status of both threads in the replication process.

  • 17.5.3: Is it possible to set the amount of acceptable lag?

  • 17.5.4: Does MySQL Load Balancer handle load balancing based on CPU load, memory load or I/O load?

Questions and Answers

17.5.1: The current description says that the load balancer is for read-only operation. Does that mean that MySQL Load Balancer will not accept update statements for the slaves?

No. Currently, the MySQL Load Balancer doesn't prevent you from making modifications on the slaves. The read-only description is being used to indicate that you should only use this solution for sending quries to existing slave hosts.

17.5.2: The MSQL Load Balancer is listed as being 'slave state aware'. Do you check the status of both threads in the replication process.

Yes. the monitor module runs SHOW SLAVE STATUS and checkes the status of the replication process. If there is a problem, either because the slave has lagged too far behind the master, or because the query thread has stopped, then the slave will be taken out of the list of available slaves for distributing queries.

17.5.3: Is it possible to set the amount of acceptable lag?

Yes, you can set the lag time by editing the time within the load balancer Lua script. Edit the file share/mysql-load-balancer/ro-balance.lua and change the line: 

max_seconds_lag = 10,      -- 10 seconds

Altering the 10 seconds to the lag time that you want to support.

17.5.4: Does MySQL Load Balancer handle load balancing based on CPU load, memory load or I/O load?

Currently we use indirect measurements and balance the distribution of queries by looking at the replication status of the slave nodes. Since the distribution of work is written using Lua, it is possible to use a number of different criteria. Using more complex criteria will be possible in the future.