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CICS DB2CONN has two limit value, TCBLIMIT and THREADLIMIT, is this true that these two value should be greater than the CICS MXT (max task) value?

Ondemand
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  • What does the documentation say? – Bill Woodger Apr 14 '16 at 07:05
  • This may be useful, http://www.ibm.com/support/knowledgecenter/SSGMCP_5.1.0/com.ibm.cics.ts.resourcedefinition.doc/resources/db2conn/dfha4_connattr.html, but we don't know what you specifically have at your site. – Bill Woodger Apr 14 '16 at 11:07
  • Thanks @BillWoodger, I've read that doc before I posted my question here, IBM manual didn't mention about the relationship between TCBLIMIT and CICS MXT – Ondemand May 10 '16 at 02:46

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No its not true that these two values should exceed MXT.

TCBLIMIT controls the maximum number of L8 TCBs that can concurrently establish a connection to DB2. As MXT controls the maximum number of user tasks in the CICS region at any one time you're not going to see more than MXT task wanting to connect to DB2. This results in DB2 waits. Interestingly, as DB2 threads use L8 TCBs so the MAXOPENTCBS SIT parameter also has an affect on the total number of tasks that can use DB2 concurrently.

THREADLIMIT on the other hand controls the number of threads active in the POOL or per DB2ENTRY. This is often mis-configured such that the total number defined exceeds TCBLIMIT

When defining the TCBLIMIT you should take a holistic view at the DB2 level. You'll need to understand the DB2 CTHREAD limit and then determine the concurrency requirements across all address spaces that are using the DB2. If you don't, and you set TCBLIMIT too high, you'll hit the DB2 CTHREAD limit which will result in delays.

There is an IBM red paper on CICS, DB2 and thread safety that provides guidance on this subject: http://www.redbooks.ibm.com/abstracts/redp4860.html?Open

Please feel free to come back to me if you have any further questions.

Arndt Eade
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