Readconnroute
Readconnroute
This document provides an overview of the readconnroute router module and its intended use case scenarios. It also displays all router configuration parameters with their descriptions.
Overview
The readconnroute router provides simple and lightweight load balancing across a set of servers. The router can also be configured to balance connections based on a weighting parameter defined in the server's section.
Note that *readconnroute balances connections and not statements. When a client connects, the router selects a server based upon the router configuration and current server load, but the single created connection is fixed and will not be changed for the duration of the session. If the connection between MaxScale and the server breaks, the connection can not be re-established and the session will be closed. The fact that the server is fixed when the client connects also means that routing hints are ignored.
Warning: readconnroute
will not prevent writes from being done even if you
define router_options=slave
. The client application is responsible for
making sure that it only performs read-only queries in such
cases. readconnroute
is simple by design: it selects a server for each
client connection and routes all queries there. If something more complex is
required, the readwritesplit router is usually the right
choice.
Configuration
For more details about the standard service parameters, refer to the Configuration Guide.
Router Options
router_options
can contain a comma separated list of valid server
roles. These roles are used as the valid types of servers the router will
form connections to when new sessions are created.
Examples:
router_options=slave router_options=master,slave
Here is a list of all possible values for the router_options
.
Role | Description |
---|---|
master | A server assigned as a master by one of MariaDB MaxScale monitors. Depending on the monitor implementation, this could be a master server of a Master-Slave replication cluster or a Write-Master of a Galera cluster. |
slave | A server assigned as a slave of a master. If all slaves are down, but the master is still available, then the router will use the master. |
synced | A Galera cluster node which is in a synced state with the cluster. |
running | A server that is up and running. All servers that MariaDB MaxScale can connect to are labeled as running. |
If no router_options
parameter is configured in the service definition,
the router will use the default value of running
. This means that it will
load balance connections across all running servers defined in the servers
parameter of the service.
When a connection is being created and the candidate server is being chosen, the list of servers is processed in from first entry to last. This means that if two servers with equal weight and status are found, the one that's listed first in the servers parameter for the service is chosen.
Examples
The most common use for the readconnroute is to provide either a read or write port for an application. This provides a more lightweight routing solution than the more complex readwritesplit router but requires the application to be able to use distinct write and read ports.
To configure a read-only service that tolerates master failures, we first need to add a new section in to the configuration file.
[Read-Service] type=service router=readconnroute servers=slave1,slave2,slave3 router_options=slave
Here the router_options
designates slaves as the only valid server
type. With this configuration, the queries are load balanced across the
slave servers.
For more complex examples of the readconnroute router, take a look at the examples in the Tutorials folder.
Router Diagnostics
The router_diagnostics
output for readconnroute has the following fields.
queries
: Number of queries executed through this service.
Limitations
-
Sending of binary data with
LOAD DATA LOCAL INFILE
is not supported. -
The router will never reconnect to the server it initially connected to.