Reducing Client Connection Delays When DNS Is Unresponsive

(Doc ID 1449843.1)

Last updated on NOVEMBER 13, 2017

Applies to:

Oracle Net Services - Version 11.2.0.2 to 12.1.0.2 [Release 11.2 to 12.1]
JDBC - Version 11.2.0.4.0 to 11.2.0.4.0 [Release 11.2]
Oracle Net Services - Version 11.2.0.1 to 11.2.0.1 [Release 11.2]
Oracle Database - Enterprise Edition - Version 11.2.0.3 to 11.2.0.3 [Release 11.2]
Oracle Database - Enterprise Edition - Version 12.1.0.2 to 12.1.0.2 [Release 12.1]
Information in this document applies to any platform.

Goal

In Oracle RAC clients frequently use DNS to resolve a scan name to one of three scan listener IP addresses.

Scan address setup in DNS

[mseibt@netbde]$ nslookup scan
..
Name: scan.us.oracle.com
Address: 10.141.155.187
Name: scan.us.oracle.com
Address: 10.141.155.185
Name: scan.us.oracle.com
Address: 10.141.155.186


In situations where the primary nameserver is down, to perform maintenance for example, client connectivity and any operation involving resolution of the scan name may experience a delay. The delay is at the OS level since the DNS query must timeout and then failover to the secondary or backup nameserver.

There are multiple areas that can be tuned to mitigate client connection delays when a nameserver is down. These tips and solutions are also helpful in non-RAC environments.

Solution

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