Daylight Saving Time changes effect on CICS Transaction Server

Abstract
For many countries Daylight Saving Time (DST) changes the last Sunday in October or the first Sunday in November. You would like to understand the impact that the DST time change has on CICS® Transaction Server. You would also like to know when DST will begin and end in your country, and the action that you will need to take.

Content
Beginning in 2007, most of the United States, 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 U.S., each time zone switches at a different time.

In the European Union, 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 elsewhere in the world.
What will happen if you fail to update your systems?
Systems or 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.

In short, if your system makes date or time calculations, you might experience calculation errors.

See Effect of daylight saving time changes in the CICS information center for more details.
How do you update CICS to reflect the DST time change?
If you change the MVS® system time-of-day at any other time than midnight and you have a 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 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.

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 created at midnight. A DFHIC0801 message is created anytime the CICS local date and time is altered, such as:
• at midnight when the MVS system time-of-day is reset to zero
• at PERFORM RESET or recycle time when CICS local time-of-day and MVS system time-of-day are synchronized

CICS Transaction Server for VSE/ESA™ V2.3 and V1.1 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.

Cross Reference information
Segment Product Component Platform Version Edition
Host Transaction Processing CICSPlex SM Availability z/OS 2.2, 2.3, 3.1

Product Alias/Synonym
CICS/VSE CICS VSE CICS/TS CICS TS CICS Transaction Server

Effect of day-light saving time changes :

Many countries operate a policy of adjusting clocks by one hour at the beginning and end of Summer to effect what is commonly referred to as ‘day-light saving’. These time changes are also applied to the local time held in computers. Generally, most hardware (TOD) clocks are set to Greenwich Mean Time (GMT), with an offset value to indicate local time. It is this offset value that is adjusted when making day-light saving time changes, while the hardware clock remains unaltered.

Adjusting local time:
When setting clocks forward or back an hour to adjust for Summer and Winter time while a CICS® region is running, use the CEMT PERFORM RESET (or EXEC CICS RESETTIME) command to ensure that CICS immediately resynchronizes its local time with that of the MVS™ TOD clock.
Note: CICS obtains and stores the local time offset only at start up, and when the CEMT PERFORM RESET command executes. Use the CEMT PERFORM RESET command immediately whenever you change the system date or time-of-day while CICS is running, to ensure that the correct local time is used by all CICS functions, including the API. Whenever an application program issues an EXEC CICS ASKTIME command, CICS obtains the current time from the MVS TOD clock, and modifies this by the stored local time difference. CICS then updates the EIBTIME field in the exec interface block with the local time.

Time stamping log and journal records:
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.
CICS time-stamps the data it writes to the system log as follows:
• System log block headers are time-stamped with both the machine clock (STCK) value and local time
• System log records are time-stamped with the machine clock (STCK) value only.
For general logs, in addition to time-stamping as in system logs, CICS also includes local time in the journal records.
During a restart, for system recovery purposes, CICS reads the youngest—most recently written—record from the primary log stream. Thereafter, CICS uses only direct reads using block ids and does not rely upon time stamps. CICS also uses direct read with block ids to retrieve the logged data for transaction backout purposes, again without any dependence on time stamps.
Operating a recovery process that is independent of time-stamps in the system log data ensures that CICS can restart successfully after an abnormal termination, even if the failure occurs shortly after local time has been put back.

Thanks & Regards,Ram