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SAP Note 7417 - Conversion between standard time anddaylight saving time

Note Language: English Version: 24 Validity: Valid Since 14.11.2011

Summary

Symptom

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.

Other terms

Time-conversion, daylight saving time, standard time, DST

Reason and Prerequisites

The following points are to be considered in this context:

o During the time conversion, the local time changes in one step,whereas UTC (Universal Time Coordinated, Greenwich Mean Time, or

GMT) changes constantly.

o 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):

o 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.

o If you have scheduled cyclical background jobs, errors may occur.

The same applies for cyclical ABAP programs in the background or

similar.

o Backup and archive operations may become inconsistent.

o Additional time-controlled operations to consider:

- Buffer synchronization

- Refresh timer in the graphics module

- Timeout monitoring

o Timestamp-based dependencies may become inconsistent: This affects

EU objects, DDIC-objects, objects in applications.

If the system time is UTC (Coordinated Universal Time), this problem doesnot occur and there is no reason for you to shut down the system when there

is a switch from daylight saving time to standard time.

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Solution

The SAP recommended procedure for time conversion is described below.

Refer to the following notes.

o 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!

o 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.

o 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

o all processes that are active in the SAP system (application

server, database, DB listener and so on) must the same local timezones (see note 398374).

o 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 time-critical

applications, the system should be stopped during the conversion. In this

case, time-critical means that an application is instructed to use two time

stamps (sy-uzeit, sy-datum) to calculate a time difference. During the

switch from standard time to daylight saving time, the time difference

calculation would return a value that is one hour too much. If the

calculation of time differences is carried out using UTC time stamps, this

is not a problem.

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 moreinformation, see Note 102088.

If, for example, the hour from 2:00 to 3:00 occurs twice when you change to

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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 6.40It 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 higherIt 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 clockof 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.

o 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.

o 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

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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:

o Can a deviation from the official time of up to 30 minutes be

tolerated?

o Does the application program contain real time components (for

example for time measurements)?

o Are ABAP time stamps ("GET TIME STAMP FIELD ...") and ABAP system

time compared (SY-DATUM/SY-UZEIT)?

o Are ABAP user time (SY-DATLO/SY-TIMLO) and ABAP system time

compared (SY-DATUM/SY-UZEIT)?

o 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 :

o All processes in your SAP system (application server, database,

database listener, and so on), must have local time zones that are

technically absolutely identical (refer to Note 398374 for more

information).

o 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 deactivatethe extended time function.

The extended time function is controlled using the profile parameter

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zdate/DSTswitch_contloctime, which has the default value "on".

Refer to Notes 102088 and 950114 for this.

Header Data

Release Status: Released for Customer

Released on: 14.11.2011 15:01:06

Master Language: German

Priority: Recommendations/additional info

Category: Workaround for missing functionality

Primary Component: BC-ABA-LA Syntax, Compiler, Runtime

Secondary Components:

BC-SRV-TIM-TZ Time zones

The Note is release-independent

Related Notes

Number Short Text

1735719 Leap seconds and the SAP system

1454474 0FI_GL_14: Problems with change to daylight saving time

1375438 Globalization Collection Note

398374 Problems when converting summer time winter time

391658 iSeries: Daylight saving time/standard time change

157704 Change dayl. sav.time/std.time and loc.crcy chang.

102088 Reducing downtime when changing from summer to winter time

15913 Timezone problems (local vs. global time)