IBM Support

Daylight Saving Time changes effect on CICS TS

Question & Answer


Question

How does the Daylight Saving Time (DST) time change affect CICS Transaction Server for z/OS and z/VSE (CICS TS)? I would like to know when DST begins and ends in my country, and if there are any actions that I will need to take for CICS when the time changes.

Answer

Most of the United States (US), Canada, Bermuda, and Bahamas begins DST at 2:00 a.m. on the second Sunday in March and reverts to standard time on the first Sunday in November. In the US, each time zone switches at a different time.

In the European Union (EU), Summer Time begins and ends at 1:00 a.m. Universal Time (Greenwich Mean Time). It begins the last Sunday in March and ends the last Sunday in October. In the EU, all time zones change at the same moment.

See more information about daylight savings time elsewhere in the world.


What will happen if you fail to update your CICS time?

If the CICS time is not synchronized with the z/OS time immediately whenever you alter the system date or time of day in the MVS TOD clock while CICS is running, applications that rely on date or time processing functions could make incorrect calculations. Calendar, scheduling, or synchronizing problems could arise where systems use date or time stamps, or if dates or times are processed or manipulated in any way.

The section on Time stamping log and journal records in the CICS documentation explains why a local time change, forwards or backwards, has no effect on CICS logging or journaling, or on CICS restarts, but could affect the operation of utility programs such as DFHJUP. If using user or vendor written journal utilities or DFHJUP with SUBSYS, when adjusting clocks backwards, it says you might need to stop CICS regions until the new local time passes the old time at which the change was made. See Effect of daylight saving time changes in the CICS documentation for more details.

If your CICS regions run applications that do EXEC CICS STARTs or EXEC CICS DELAYs or EXEC CICS POSTs that specify a TIME (rather than an INTERVAL), and that time is calculated from EIBTIME plus some amount of time, then those STARTs and DELAYs and POSTs will expire immediately if the CICS time does not match the z/OS time. This can cause various problems like application loops and excessive SMF data recording that can cause the CICS region to become unresponsive.


How do you update CICS to reflect the DST time change?

In July 2012, a new IMMEDIATE option for CICS system initialization (SIT) parameter AUTORESETTIME became available. When using this option, CICS synchronizes the CICS time with the z/OS time immediately whenever you alter the system date or time-of-day in the MVS TOD clock while a CICS region is running. CICS does this by issuing a PERFORM RESET command.

The IMMEDIATE option for AUTORESETTIME parameter is in the base code of CICS TS V5.1 and higher. You will need to apply a PTF to get the new functionality if using a release lower than CICS TS V5.1:

  • CICS TS 4.2 - PTF UK78430 for APAR PM61466

  • CICS TS 4.1 - PTF UK77263 for APAR PM52109

  • CICS TS 3.2 - PTF UK78322 for APAR PM52172

AUTORESETTIME=IMMEDIATE is the default and recommended value.

If you set AUTORESETTIME to YES, CICS automatically issues a PERFORM RESET command to synchronize the CICS time-of-day with the system time-of-day at the next local midnight. That is, if the CICS time-of-day differs from the system time-of-day by more than 30 minutes. So when using this option, if you reset the MVS system time just before midnight then you will NOT have to enter CEMT PERFORM RESET in your CICS regions. Note: Setting clocks back might cause end-of-day statistics to be written twice.

If you set AUTORESETTIME to anything other than IMMEDIATE and you change the MVS system time-of-day at any other time than midnight while CICS region running, then you should immediately enter a CEMT PERFORM RESET (or EXEC CICS RESETTIME) command to synchronize the CICS time-of-day with the system time-of-day. You should not wait until midnight to synchronize the CICS and system time-of-day. If CICS is down when you change the system time-of-day then the CICS time-of-day will be reset automatically when you bring CICS back up.

If you set the CICS system initialization parameter AUTORESETTIME to NO or let it default to NO, CICS does not automatically update the CICS time-of-day. CICS issues message DFHAP1500 to indicate that a CEMT PERFORM RESET command is required to synchronize the CICS time-of-day with the system time-of-day.

The system time-of-day and CICS time-of-day need to be synchronized on your CICSPlex SM CMAS and WUI server address spaces as well. Failure to do so could result in symptoms such as abend AICG or BATCHREP commands receiving timeout.

To verify if CICS is using the correct time, you can look at the SYSLOG. If the time stamps of the MVS messages do not coincide with the time stamps of the CICS messages, then they are out of sync. Another option could be to check the DFHIC0801 message which is created anytime the CICS local date and time is altered, such as when the MVS system time-of-day is reset to zero at midnight or when the CICS local time-of-day and MVS system time-of-day are synchronized:

  • when your region is down and you bring it back up (recycle time)

  • when you enter CEMT PERFORM RESET

  • when CICS issues the PERFORM RESET because you specify AUTORESETTIME=IMMEDIATE or AUTORESETTIME=YES

CICS Transaction Server for VSE/ESA V1.1.1 and CICS Transaction Server for z/VSE V2.1 and V2.2 do not support the AUTORESETTIME system initialization parameter or issue message DFHAP1500. Therefore, a manual reset is required. Either restart your CICS region or enter a CEMT PERFORM RESET command to allow the CICS and system clocks to synchronize.

[{"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSGMGV","label":"CICS Transaction Server"},"Platform":[{"code":"PF035","label":"z\/OS"}],"Component":"","Version":"","Line of Business":{"code":"LOB35","label":"Mainframe SW"}}]

Product Synonym

CICS/TS CICSTS CICS TS CICS Transaction Server

Document Information

Modified date:
07 November 2017

UID

dwa1177632