Affinity enables you to specify at connection time that the connector
should forward the connection to a particular host or service for reads,
if the service is available. For example, within
user.map:
user password west east
Defines a user that uses the
west service, but prefers
being routed to the east service
for reading from a Replica.
Affinity can also specified within the connection string:
jdbc:mysql://connector1:3306/database?affinity=host3&qos=RO_RELAXED
Additionally, affinity JDBC options can be set globally via the
tpm command option
connector-affinity.
The read affinity setting supports multiple dataservices with ordering and exclusion.
You may fine-tune the affinity by specifying an ordered list of dataservice names.
The affinity string is an ordered list of
dataservice names, separated by commas, where the first dataservice
entry will be the one used by default. If the first dataservice in
the list is not available, the connector will use the next one
listed, and so forth.
Dataservices not specified in the list, if any, will be used last and randomly.
It is also possible to exclude one or more dataservices by adding a hyphen ("-") in front of the dataservice name.
Affinity can also be combined with other node selection, such as QoS.
For example, by combining the affinity and
RO_RELAXED, then the specified
Replica will be used first, if the load-balancer setting matches, then
another Replica within the same service, and finally the Primary. For
example, in a dataservice with three nodes, where
node1 is the Primary:
shell> mysql -h127.0.0.1 -P3306 databasename@qos=RO_RELAXED\&affinity=node2
Would use node2 first, then
node3, and finally
node1 if the others are not
available.
Within a composite dataservice, you cannot specify a specific host. You can only specify a physical dataservice within the composite dataservice. For example in a composite service with east and west physical dataservices:
shell> mysql -h127.0.0.1 -P3306 databasename@qos=RO_RELAXED\&affinity=east
Additionally, the user.map can be configured to
direct specific users to a Replica by using the
@direct keyword. For example, the
following line in user.map will always direct the
user to a Replica, ignoring latency and load balancing settings:
@direct readme