Client-side Load Balancing

A new case study has been published in Metalink about how to configure a high connect load environment. If you have an environment where bursts of logon activity appears sometimes and your tns listener is unable to cope with the demand then you can take a look at the note to see possible solutions. It is a simple note that basically describes how the tns listener works and what to when the listener cannot respond to connection requests.

There are mainly two solutions suggested:

1. Increasing the number of listeners
2. Using shared server

Increasing the number of listeners is the first logical solution that comes up. Because a single listener process can handle a limited number of requests at one time, multiple listener processes can handle many more requests. When you configure multiple listeners you also need to change the tns entries in your clients. The sample tns entry provided in that note is this:

GEORGE=
(DESCRIPTION=
(LOAD_BALANCE=ON)
(FAILOVER=ON)
(ADDRESS=(PROTOCOL=TCP)(HOST=george.us.oracle.com)(PORT=1521)
(ADDRESS=(PROTOCOL=TCP)(HOST=george.us.oracle.com)(PORT=1522)
(ADDRESS=(PROTOCOL=TCP)(HOST=george.us.oracle.com)(PORT=1523)
(ADDRESS=(PROTOCOL=TCP)(HOST=george.us.oracle.com)(PORT=1524)
(CONNECT_DATA=(SERVICE_NAME=V10R2.us.oracle.com)))

This ensures that connections are balanced between the specified ports, meaning different listener processes.

But there is one restriction that is not mentioned in the case study. If you have clients using Net8 (not higher versions) like Forms6i applications, the LOAD_BALANCE parameter does not exist, so you cannot load balance client connections using this entry. If you have such clients you need to use description lists in your tns entry as described in Metalink note 67137.1. The tns entry for load balancing in Net8 is like this:

TEST=
(DESCRIPTION_LIST=
(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)(HOST=host1)(PORT=1521)
)
(CONNECT_DATA=(SID=TEST))
)
(DESCRIPTION=
(ADDRESS=
(PROTOCOL=TCP)(HOST=host1)(PORT=1522)
)
(CONNECT_DATA=(SID=TEST))
)
)

Sure it is better to fix the application to correct the logon burst problem but in case you have a situation where you cannot fix the application for any reason it is good to be aware of these solutions.