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From Joerg von Frantzius <joerg.von.frantz...@artnology.com>
Subject Re: [DISCUSS} Server TimeZone
Date Fri, 09 Feb 2007 10:15:23 GMT
Hello Erik,

this seems to be connected to thread Transaction Manager and JCA 
<http://www.jpox.org/servlet/forum/viewthread?thread=4099>, where it 
seems you proposed to associate a single PersistenceManagerFactory with 
multiple DBs. As a PMF only has properties to connect and authenticate 
with a single DB (URL, username/pw), I think the spec implicitly defines 
that a PMF can be connected to a single DB only.

So it seems to me your question implies some fundamental conceptual change?


Erik Bengtson wrote:
> Craig, I understand that server means the backend database server. what it we
> have multiple backend db servers?
> Use case with multiple dbs:
> SELECT FROM db1.classA WHERE classA.time > datetime() && classB.time >
> datetime() VARIABLES db2.classB
> The first datetime() is evaluated by db1, while the second by db2.
> Quoting Craig L Russell <Craig.Russell@Sun.COM>:
>> Here is a proposal to add the ability of a user to get the time at
>> the server in a portable way.
>> This should allow an application to avoid time skew by using the time
>> as seen by a single source, the server to which the
>> PersistenceManagerFactory is connected.
>> <proposed>
>> 11.1
>> ...
>> ServerTimeZoneID: the time zone ID of the server to which this
>> PersistenceManagerFactory is connected, for use with the
>> PersistenceManager method getServerDate
>> If ServerTimeZoneID is specified, the value must correspond to a
>> valid time zone ID as returned by TimeZone.getAvailableIDs(). The
>> implementation uses the ServerTimeZoneID to implement the
>> getServerDate method. If ServerTimeZoneID is not specified, the
>> implementation might use proprietary methods to determine the time
>> zone in which the server is located. If ServerTimeZoneID is not
>> specified, and the implementation cannot or does not use proprietary
>> methods to determine the server time zone, then the default time zone
>> ID of the Java VM is used.
>> 12.17 Server Date
>> java.util.Date getServerDate();
>> Time skew is a phenomenon in which machines connected together in
>> client/server configurations might have clocks that are not perfectly
>> synchronized, and the time as seen by different clients might differ.
>> In order for the application to avoid time skew, this method can be
>> used to acquire a Date instance corresponding to the UTC Date as seen
>> by the server. Clients using this method can order their operations
>> according to a single time source.
>> Implementations use the setting of the server time zone to prepare a
>> Date instance that represents UTC time on the server.
>> </proposed>
>> Craig Russell
>> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
>> 408 276-5638 mailto:Craig.Russell@sun.com
>> P.S. A good JDO? O, Gasp!

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