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  • October 21, 2016

WebLogic Server Datasource Gradual Draining

Stephen Felts

In October 2014, we delivered Oracle WebLogic Server 12.2.1 as part of the
overall Oracle Fusion Middleware 12.2.1 Release and October 2015 we delivered
the first patch set release This week, the second patch set is available.   New
WebLogic Server installers are now posted on the Oracle Technology Network and Oracle Software Delivery Cloud, and
new documentation has been made
available. There are a couple of new
datasource features hidden there. One of
them is called “gradual draining.”

When planned maintenance occurs on an Oracle RAC configuration, a planned
down service event is processed by an Active GridLink data source using that
database. By default, all unreserved connections in the pool are
closed and borrowed connections are closed when returned to the pool. 
This can cause an uneven performance because:

· New connections need to be created on the
alternative instances.

· A logon storm on the other instances can occur.

It is desirable to gradually drain connections instead of closing them
all immediately. The application can define the length of the draining period
during which connections are closed. It
is configured using the weblogic.jdbc.drainTimeout value in the connection
properties for the datasource. As usual,
it can be set in the console, EM, or WLST. The following figure shows the administration console.

The result is that connections are closed in a step-wise fashion every 5
seconds. If the application is actively
using connections, then they will be created on the alternative instances at a
similar rate. The following figure shows
a perfect demonstration of draining and creating new connections over a 60 second period using a sample
application that generates constant load.  Without gradual draining, the current capacity on the down instance would drop off immediately similar to the LBA percentages and connections would be created on the alternative instance as quickly as possible.

There are quite a few details about the interaction with RAC service
life-cycle, datasource suspension and shut down, connection gravitation,
etc. For more details, see Gradual Draining in Administering JDBC
Data Sources for Oracle WebLogic Server

Like several other areas in WLS datasource, this feature will be automatically
enhanced when running with the Oracle Database 12.2 driver and server. More about that when the 12.2 release ships.

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