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POLoad balancing Cascading JDBCTap for MySQL
 

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  1. POLoad balancing Cascading JDBCTap for MySQL
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    <p>I am considering writing a Cascading application that issues SELECT statements to MYSQL databases where each query can return millions of rows.</p> <p>Each database exists on N slaves and one master, as shown here: <a href="http://dev.mysql.com/doc/refman/5.0/en/replication-solutions-scaleout.html#figure_replication-scaleout" rel="nofollow">http://dev.mysql.com/doc/refman/5.0/en/replication-solutions-scaleout.html#figure_replication-scaleout</a></p> <p>In JDBCTap, I see that we can only pass one hostname: this means that all my mappers would try and connect to a single slave (while the other (N-1) slaves are idle).</p> <p>Assuming there is no load balancer in front of the slaves, is there a JAVA package/module/proxy (or better, a customized JDBCTap implementation) I can use that can spread out the connection of the mappers across the N slaves?</p> <p>A sample script using a hardware proxy that seems to do this is detailed here: <a href="http://blog.netoearth.com/html/201006/building-a-mysql-load-balancing-proxy-with-trafficscript.htm" rel="nofollow">http://blog.netoearth.com/html/201006/building-a-mysql-load-balancing-proxy-with-trafficscript.htm</a></p> <p>If such a thing does not exist, I would have to create my own JDBCTap (that spreads out the connection from the mappers across the N slaves) using the following algorithm:</p> <ol> <li>Keep a list of the N slaves on an external database (anything that supports concurrent writes/updates well)</li> <li>Have a counter of mappers that have connected against each slave</li> <li>Every-time a mapper needs to connect to a slave, it queries this database to find out the slave that is least loaded(has min count of mappers connected to it). Random tie-break on collision.</li> </ol> <p>Does this sound like a good idea? What could be the external database "that supports concurrent writes/updates well" that I referred to above? (Cassandra, VoltDB, etc)</p>
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