If you are adding DB2 Server for VSE work to an existing CICS environment, consider increasing the CICS DFHSIT macro AMXT value. The optimal level of CICS subtasking may now be higher than it was. Each active ISQL user requires two active tasks within CICS. If the AMXT limit is reached, response time is adversely affected.
| Note: | If you are using the new CICS Transaction Server under VSE/ESA 2.4, the DFHSIT AMXT parameter is obsolete. Please see the CICS TS documentation for more information. |
Use transaction name ISQ2 rather than CISQ for ISQL. The ISQL transaction will attempt to start a second transaction called ISQ2. If it cannot find ISQ2 it will look for the CISQ transaction. Using the name ISQ2 avoids the additional processing involved in searching for both ISQ2 and CISQ. (The ISQL transaction first looks for a second transaction whose name is constructed by replacing the last character of the first transaction ID with 2. In this case it would be ISQ2.)
Consider limiting the number of concurrent ISQL users. If the database manager is only used from the CICS environment through ISQL, you can limit the number of concurrent users by limiting the number of links to the application server when you start the DB2 Server for VSE online support (CIRB transaction).
If you plan to use the database manager from the CICS environment through both ISQL and preplanned transactions, you can do this using the CICS CMXT parameter. This is done by assigning the CISQ transaction to its own CICS class and setting CMXT for that class to the desired limit.
Do not place a CMXT limit on the ISQL transaction ID. It may cause problems with long queries. The ISQL transaction will temporarily end in the middle of a long query, leaving the CISQ transaction active while it waits for a reply from the application server. If more ISQL users logon, the number of ISQL transactions can reach the CMXT limit. When the CISQ transaction eventually gets a reply from the server, it try's to restart its partner ISQL transaction. This will fail if the CMXT limit has been reached.
You can use CMXT to allocate CICS-DB2 Server for VSE links for CICS production work that requires access to DB2 Server for VSE data. For example, if 6 CICS-DB2 Server for VSE links are defined, and CMXT limits the number of ISQL users to 4, at least 2 links are always available for other DB2 Server for VSE requests.
Instead of limiting the total number of ISQL users, you can also limit the number of ISQL users by group. For more information refer to the DB2 Server for VSE System Administration manual.
Consider using AUXILIARY storage if you expect to run large routines. All ISQL routines are read into CICS temporary storage (either MAIN or AUXILIARY) before the first command in the routine is run. Using MAIN temporary storage improves performance but uses more virtual storage. Using AUXILIARY temporary storage slightly degrades performance, but reduces the amount of virtual storage required.
To use MAIN storage, code TSP=1$ on the CICS SIT or to use AUXILIARY storage, code TSP=2$.