To balance connections to instances more evenly, different selection strategies can be used. The following table describes the currently available selection strategies and any relevant configuration parameters for each strategy.
| Host Selection Strategy | Configuration Parameter | Description | Default Value | Available Since Version |
|---|---|---|---|---|
random |
This strategy does not have configuration parameters. | The random strategy is the default selection strategy. When selecting a host, a random host will be selected from the list of available hosts. | N/A | 2.0.0 |
leastConnections |
This strategy does not have configuration parameters. | The least connections strategy will select instances based on which database instance has the least number of currently active connections. Note that this strategy is only available when internal connection pools are enabled - if you set the connection property without enabling internal pools, an exception will be thrown. | N/A | 2.2.0 |
roundRobin |
See the following rows for configuration parameters. | The round robin strategy will select an instance by taking turns with all available database instances in a cycle. A slight addition to the round robin strategy is the weighted round robin strategy, where more connections will be passed to instances based on user specified connection properties. | N/A | 2.2.5 |
roundRobinHostWeightPairs |
This parameter value must be a string type comma separated list of database host-weight pairs in the format <host>:<weight>. The host represents the database instance name, and the weight represents how many connections should be directed to the host in one cycle through all available hosts. For example, the value instance-1:1,instance-2:4 means that for every connection to instance-1, there will be four connections to instance-2. Note: The <weight> value in the string must be an integer greater than or equal to 1. |
null |
||
roundRobinDefaultWeight |
This parameter value must be an integer value in the form of a string. This parameter represents the default weight for any hosts that have not been configured with the roundRobinHostWeightPairs parameter. For example, if a connection were already established and host weights were set with roundRobinHostWeightPairs but a new instance was added to the database, the new instance would use the default weight. Note: This value must be an integer greater than or equal to 1. |
1 |
||
fastestResponse |
See the following rows for configuration parameters. | The fastest response strategy identifies the fastest response host, then stores this host in a cache for future use. Note: The Fastest Response Strategy plugin must also be loaded into the plugins list by setting the plugins connection configuration parameter to include the fastestResponseStrategy plugin code. |
N/A | 2.3.2 |
responseMeasurementIntervalMs |
Interval in millis between measuring response time to a database node. | 30000 |
These strategies are applicable when using the following plugins: