USER MANUALS

Connecting to Virtual DataPort Through a Load Balancer

Read this section when the JDBC client is connecting to Virtual DataPort through a load balancer or another intermediate resource that holds a pool of connections to Virtual DataPort.

The table Parameters of the JDBC driver useful to set-up a cluster of Denodo servers lists the parameters of the URL that are useful when connecting to Virtual DataPort through a load balancer:

Parameters of the JDBC driver useful to set-up a cluster of Denodo servers

Parameter of the URL

Description

reuseRegistrySocket

Important: set this property to false when connecting to Virtual DataPort through a load balancer.

If false, the requests will be more evenly distributed across the Virtual DataPort servers of the cluster than if the property is not set or set to true.

Default value: true

pingQuery and pingQueryTimeout

Important: only use these two properties if the load balancer or the client will execute a ping query without support to set a timeout for that query.

When a client executes the query set on the parameter pingQuery, the JDBC driver returns an error if that query does not finish in the number of milliseconds set on pingQueryTimeout.

See below for a more detailed explanation of these properties.

Default value for both parameters: <empty>

Sample URL for JDBC applications that connect to Virtual DataPort through a load balancer:

jdbc:vdb://acme:9999/support?reuseRegistrySocket=false

Sample URL for JDBC applications with the parameters pingQuery and pingQueryTimeout:

jdbc:vdb://acme:9999/admin?reuseRegistrySocket=false&pingQuery=SELECT 1&pingQueryTimeout=1000

With the URL above, if the query SELECT 1 does not finish in one second, the driver returns an error.

You need to add the parameters pingQuery and pingQueryTimeout to the connection URL if the load balancer or the client meet these conditions:

  • It will execute a ping query to check that the Virtual DataPort server is alive, or a connection to it is still valid.

  • And it does not support setting a timeout for that ping query.

At runtime, when the JDBC driver receives the query set on the parameter pingQuery, it will wait for a maximum of pingQueryTimeout milliseconds for the query to finish. If the query does not finish in that time, the driver will return an error, which will indicate the client or the load balancer that the connection is no longer valid. A connection to a Virtual DataPort server can become invalid when it has timed out or dropped by a firewall.

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