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After a session command fails on all connected slaves but succeeds on the master, the servers that failed are discarded from the pool of valid servers. If there are available servers, they will be taken into use when the next read query is performed. When a query is routed to an unconnected slave, it is taken into use and the session command history is replayed. If the execution of the history failed and there were more session commands to be executed, any queued queries would get lost. This is due to a missing check that would detect the fact that the server has been discarded.
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.
We're also on the #maria and #maxscale channels on FreeNode.
Please report all feature requests, improvements and bugs in the MariaDB Jira.
Documentation
For information about installing and using MaxScale, please refer to the documentation. The official documentation can be found on the MariaDB Knowledge Base.
- MariaDB MaxScale 2.1 Documentation
- MariaDB MaxScale 2.0 Documentation
- MariaDB MaxScale 1.4 Documentation
The module and configuration documentation can be found in the Documentation directory of the source tree.
Contributing Code
Read the Contributing page on the wiki for more information on how to do pull request and where to do them.