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Conversion between standard time and daylight saving time

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Conversion between standard time and daylight saving time
Stechies

You search for information about the operation of SAP systems during the time conversion from standard time to daylight saving time or from daylight saving time to standard time.

The following points are to be considered in this context:

  • During the time conversion, the local time changes in one step, whereas UTC (Universal Time Coordinated, Greenwich Mean Time, or GMT) changes constantly.
     
  • A local time zone that may also contain a daylight saving time rule (DST rule) is almost always selected as the system time for the SAP system. As a result, an SAP system that is configured in such a way is directly affected by the time conversion.

If an SAP system with a system time with daylight saving time rule runs during the time conversion, the following errors may occur. The errors are caused by the fact that the system time changes suddenly in one step (and inconsistently):
 

  • The runtime error ZDATE_LARGE_TIME_DIFF may occur. This dump informs about a difference that is too large between the ABAP system time and the database time. This difference may occur suddenly if one of the times changes suddenly in one step due to the time conversion.
     
  • If you have scheduled cyclical background jobs, errors may occur. The same applies for cyclical ABAP programs in the background or similar.
     
  • Backup and archive operations may become inconsistent.
     
  • Additional time-controlled operations to consider:

    Buffer synchronization

    Refresh timer in the graphics module

    Timeout monitoring
  • Timestamp-based dependencies may become inconsistent: This affects EU objects, DDIC-objects, objects in applications.


The SAP recommended procedure for time conversion is described below.

Refer to the following notes.

    A time difference of a few seconds can be tolerated in configuration of several computers. However, you must ensure that you NEVER set the system time of a server in the past for an active SAP system!

    If you change the system clock time by a minute or more, or make changes to the time-zone settings, you must restart the SAP system. The SAP system must not be active when you make the changes.

    Note that when the SAP system is running, all processes that are active on it (application server, database, database listener and so on) must have the same technical time zones (refer to Note 398374 for more information).


Conversion from standard time to daylight saving time

When the time is converted from standard time to daylight saving time, the clocks move forward one hour. This is not normally critical for applications. If you require the system to run without downtime, you must ensure that

  • all processes that are active in the SAP system (application server, database, DB listener and so on) must the same local time zones.
     
  • all computers active in the SAP system must be synchronized with each other to the second (Unix/Linux for example: XNTP). You have to set the time synchronization parameters so that the system time of the server is never set to a time in the past.



Restarting the computer usually solves any problems. For critical applications, the system should be stopped during the conversion.

Conversion from daylight saving time to standard time


Problems generally occur when the system switches from daylight saving time back to standard time.

For all releases, the system should be deactivated for a little over two hours, from before the final hour of daylight saving time has begun until the first hour of standard time has ended (the "double hour"). For more information, see Note 102088.
If, for example, the hour from 2:00 to 3:00 occurs twice when you change to standard time, you must deactivate the system from 01:55:00 AM until 3:05 AM. This time period has been marked with 'x' on the following time-scale. The downtime is approximately two hours and ten minutes.


1:00   1:30   2:00   2:30   2:00   2:30   3:00 official time
--+------+-----x+xxxxx+xxxxxx+xxxxxx+xxxxxx+x---

Alternative approaches to the procedure for this depend on the SAP kernel being used.

Kernel Release earlier than 6.40
It is possible under certain circumstances to reduce system downtime from a little over two hours to a little over one hour. Refer to Note 102088.

Kernel release 6.40 and higher
It is possible under certain circumstances to reduce system downtime from a little over two hours to a little over one hour. Refer to Note 102088.

In addition, a new technology is used in SAP Web Application Server ABAP as of Kernel Release 6.40, which will enable the system to continue running during the change from daylight saving time to standard time. However, you can only use this technique in very rare cases at the moment (see below for more information).

The aforementioned technique extends one hour of the kernel time (for example, 1:00 to 1:59) to two hours of the official time (for example, 1:00 to 1:59 daylight savings time and 1:00 to 1:59 standard time). This means that the time of the SAP system runs slower over two hours, but continuously.
While the 'double hour' runs twice during this two hour period, the clock of the SAP system runs at half speed, which means that only one hours appears to pass. The double hour is therefore avoided. During the first hour of the double hour, the SAP time loses time increasingly until it is 30 minutes slower than the official time, but as of the second hour, the SAP time catches up on the official time until the difference between them is zero.
As a result, the values of the ABAP system time (SY-UZEIT/SY-DATUM) do not correspond to the official time.

Whether you can allow the system to run without downtime depends on whether a 30 minute difference between the SAP time and official time is permitted for the applications that are running at that time. Each SAP application has to certify this individually. The first component certified for continued operation is the ABAP Basis. The majority of applications is not certified for continued operation. In the case of modified SAP application programs, customer programs and so on, the operator must decide whether they are suitable for continued operation.

  • If a maximum difference of 30 minutes between the SAP time and the official time is permissible, you do not have to deactivate the system.
     
  • If a maximum difference of 30 minutes between the SAP time and the official time is not permissible, you have to deactivate the system for a little over 2 hours, as described above..


Every application that is certified for continued operation writes a corresponding note that is then referred to in this note under "Related Notes".

If you are not certain that all application programs running at that time are suitable for continued operation, the best thing to do is deactivate the system for a little over two hours, as described above.

To decide whether modified SAP application programs, customer programs and so on are suitable for continued operation, the following criteria may be useful:
 

  • Can a deviation from the official time of up to 30 minutes be tolerated?
     
  • Does the application program contain real time components (for example for time measurements)?
     
  • Are ABAP time stamps ("GET TIME STAMP FIELD ...") and ABAP system time compared (SY-DATUM/SY-UZEIT)?
     
  • Are ABAP user time (SY-DATLO/SY-TIMLO) and ABAP system time compared (SY-DATUM/SY-UZEIT)?
     
  • Are times from external third-party application programs and ABAP system time compared (SY-DATUM/SY-UZEIT)?


In addition, it is recommended that you first test the respective application that has to run in this phase of this extended time, even though the test scenario is difficult to set up.

Technical prerequisites

The technical prerequisites for using this new technology are as follows :

  • All processes in your SAP system (application server, database, database listener, and so on), must have local time zones that are technically absolutely identical.
     
  • all computers active in the SAP system must be synchronized with each other to the second (Unix/Linux for example: XNTP). You have to set the time synchronization parameters so that the system time of the server is never set to a time in the past.

Deactivating the continuous switch from daylight saving time to standard time

The extended SAP time delivered with Kernel 6.40 creates a time difference between SAP time and official time already one hour before the switch .

This is not critical if you deactivate the system for a little over two hours, as recommended.

If you are using Kernel 6.40 or higher and want to reduce the downtime from a little over two hours to a little over one hour, you have to deactivate the extended time function.


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