Question & Answer
Question
Using EXTSHM with DB2® on AIX® may result in performance degradation on large systems . It is recommended to use the alternative of cataloging the database with the TCP/IP loopback method .
Cause
EXTSHM (Extended Shared Memory) is an AIX feature which can be used with DB2 on AIX. It allows local applications to establish more than 10 local database connections from a single process , a common requirement of java and other multi-threaded applications . The limit of 10 local connections from a single process is a product of DB2 's architecture and the AIX 32-bit segmented memory model , which allows a process to attach to a maximum of 11 shared memory segments .
On AIX , using EXTSHM changes the nature of the shared memory segments created by an application . In particular , there is additional processing required to detach from EXTSHM-enabled shared memory segments .
DB2 makes extensive use of shared memory . On large DB2 systems, many large memory segments are created, and DB2 processes might detach frequently from these segments depending on the configuration and the activity generated by the applications and utilities.
Answer
The use of EXTSHM is not recommended for DB2 on large systems, as this configuration commonly results in significant performance degradation . The recommended alternative approach is to catalog the database using the TCP/IP "loopback" method. Refer to the links in this document's "Related information" section for an example of how to implement loopback connections .
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Document Information
Modified date:
16 June 2018
UID
swg21191295