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March 2007 Daylight Savings Time Change Information

The US Congress changed the dates when daylight saving time starts and ends with effect from March 2007. The time zone issue affects the US and Canada primarily - other regions of the world secondarily. This page provides "unofficial and without warranty" general information, as well as links to IBM sites.

In a nutshell, the time change affects IDS versions 9.4 and 10.00 for Linux, UNIX, and Windows. IDS 10 and 9.4 will have fixpacks available for download in Dec., or customers may choose to use the JZTU utility provided by IBM on the supported platforms. IDS 7.31 is not impacted.

PUBLIC LAW 109.58.AUG. 8, 2005


(a) AMENDMENT..Section 3(a) of the Uniform Time Act of 1966 (15 U.S.C. 260a(a)) is amended.

    (1) by striking ..first Sunday of April.. and inserting ..second Sunday of March..; and

    (2) by striking ..last Sunday of October.. and inserting ..first Sunday of November...

(b) EFFECTIVE DATE..Subsection (a) shall take effect 1 year after the date of enactment of this Act or March 1, 2007, whichever is later.

(c) REPORT TO CONGRESS..Not later than 9 months after the effective date stated in subsection (b), the Secretary shall report to Congress on the impact of this section on energy consumption in the United States.

(d) RIGHT TO REVERT..Congress retains the right to revert the Daylight Saving Time back to the 2005 time schedules once the Department study is complete.

Preliminary Analysis

The date (2005-08-08) was when Bush signed it into law. Item (b) therefore places it at the later of 2006-08-08 and 2007-03-01, which means it takes effect in March 2007.

IDS (all versions) relies on the o/s for its local time in the main code, so the primary requirement is that the o/s respond to the changes (an update in the files describing time zones - if you are lucky), and secondarily that IDS is aware of the changes. The reliable way of doing that is to restart IDS after the o/s time zone information is updated. If you are lucky, the system may detect the changes on the fly and resynchronize, but I'd not bet on it.

There is a secondary area of concern with IDS 9.x and later, namely the JRE bundled with IDS as part of Krakatoa. It seems that the time zone information used by Java is embedded indelibly into the JRE, and it is hard to update it without updating the whole JRE. Add to the problem that some IDS 10.00 versions of IDS were released with IBM Hursley JREs and others (eg Solaris, IIRC) were released with native (non-Hursley) JREs because of availability issues and time pressures for the release, and we have to re-release a number of platforms with a different JRE. Further, said re-released versions will have to be installed and brought up. If you don't do date-time calculations in Java stored procedures, or logging, or any other similar activity, then the chances are you won't notice the problem. If you do time-based calculations in Java in the Server (Krakatoa), then you are vulnerable to the existing JRE not recognizing the new rules for changing time zones. Note, incidentally, that the master database for many people is the Olson database, and release 2006o (the 15th version in 2006) was recently released. That's a measure of how often details change worldwide - and it isn't much more active this year than in previous years, though it probably is a bit more active than usual.

Someone in product management would have to pontificate on release versions and dates (Editor's note: see IBM Flash Alert), but my understanding is that 10.00.xC6 due out late in 2006 will be fixed. It is not clear to me what is happening for IDS 9.40. The Cheetah version will be fixed by the time it is released GA (it most likely is fixed in Beta 1, but I don't know that for certain).

For systems with an IBM Hursley JRE, there is a utility (called JTZU or thereabouts) that changes the time zone data without mandating a reinstall of the JRE. However, it would still be advisable to restart IDS after running that. Those systems are AIX and Linux, I believe.

07 November 2006 - Jonathan Leffler

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