Re: Daylight savings time, shutting down oracle

From: <oratune_at_aol.com>
Date: Fri, 27 Oct 2000 13:31:39 GMT
Message-ID: <8tc03s$i3c$1@nnrp1.deja.com>

In article <8tbs38$epq$1_at_nnrp1.deja.com>, kpacek_at_excite.com wrote:
> I'm sysadmin for a few boxes running oracle. Some are Solaris 8,
> oracle 8.0.1 others hp-ux 10.2, oracle 7.3.4 (I think). My DBA's are
> insisting that the db's be shut down between 1:30 -3:30 am Sun, during
> daylight savings time.
>
> Is there any point to this? Can anyone describe how oracle handles
> this or point me to a resource so I can bring the information to them
> to show that there is no reason for this? It seems to me, the box
> really runs GMT behind the scenes, where there is no such thing as
> daylight savings time.
>
> Thanks
> krp
>
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> Before you buy.
>

ORACLE takes its time from the host O/S and all timestamps are generated based upon the underlying system time; unless you're running GMT then the timestamps will not be GMT but the local time. When changing from Daylight Savings Time to Standard Time the possibility exists that the same time can exist on records in the redo/archive logs both before and after the time change, which is scheduled for 2:00 AM (CDT, here in the midwest), bringing the system back to 1:00 AM (CST):

01:58:00 .....
01:59:08 .....
<time change>
01:00:00 .....
...
01:58:00 .....
...

This is not a problem when writing the redo/archive logs, but it could present difficulties when attempting to restore data/transactions to an instance and the second set of timestamped transactions is desired rather than the first. Oracle states it this way in their documentation:

Note that if your database is affected by seasonal time changes (for example, daylight savings time), you may experience a problem if a time appears twice in the redo log and you want to recover to the second, or later time. To deal with time changes, perform cancel-based or change-based recovery to the point in time where the clock is set back, then continue with the time-based recovery to the exact time.

Even Oracle does not ask that instances be shut down during time changes. I believe that your DBA's are a bit overcautious with regard to Daylight Savings Time (that, or they don't want the hassle of the recovery scenario listed above, no matter how remote that possibility may be). I have never had difficulty with keeping an instance running through Standard/Daylight/Standard time changes and I can see no reason to shut down the instances for two hours simply because the system clock is being automatically set back an hour.

--
David Fitzjarrell
Oracle Certified DBA


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Received on Fri Oct 27 2000 - 08:31:39 CDT