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The combination of only one slave being used and the slave_selection_criteria being LEAST_CURRENT_OPERATIONS can possibly cause a connection pileup on one slave server. This would skew the query distribution heavily towards the first available slave even if multiple slave were being used. Having the maximum number of slave servers to be equal to the total amount of available slaves allows for a more even and responsive distribution of the query traffic.
MaxScale by MariaDB Corporation
The MariaDB Corporation MaxScale is an intelligent proxy that allows forwarding of database statements to one or more database servers using complex rules, a semantic understanding of the database statements and the roles of the various servers within the backend cluster of databases.
MaxScale is designed to provide load balancing and high availability functionality transparently to the applications. In addition it provides a highly scalable and flexible architecture, with plugin components to support different protocols and routing decisions.
MaxScale is implemented in C and makes extensive use of the asynchronous I/O capabilities of the Linux operating system. The epoll system is used to provide the event driven framework for the input and output via sockets.
The protocols are implemented as external shared object modules which can be loaded at runtime. These modules support a fixed interface, communicating the entries points via a structure consisting of a set of function pointers. This structure is called the "module object".
The code that routes the queries to the database servers is also loaded as external shared objects and are referred to as routing modules.
An Google Group exists for MaxScale that can be used to discuss ideas, issues and communicate with the MaxScale community. Send email to maxscale@googlegroups.com or use the forum interface
Bugs can be reported in the MariaDB Corporation bugs database https://mariadb.atlassian.net/projects/MXS/issues
Documentation
For information about installing and using MaxScale, please refer to the documentation.