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From Joerg von Frantzius <joerg.von.frantz...@artnology.com>
Subject Re: [DISCUSS} Server TimeZone
Date Fri, 09 Feb 2007 16:36:21 GMT
Maybe I got something wrong here, but don't we run into a whole lot of 
other questions here? Like, when we execute a query, what DB will it be 
run on? When invoking operations on a PersistenceManager from a PMF with 
multiple databases, which DB will the resulting SQL be sent to?

Erik Bengtson wrote:
> Joerg,
>
>   
>> How do you want to configure multiple database connections per PMF
>> without extending the spec?
>>     
>
> Agreed, this has to discussed/specified in JPOX. After completed the
> implementation, I see this as a potential feature to be proposed to JDO
> standard
>
> Quoting Joerg von Frantzius <joerg.von.frantzius@artnology.com>:
>
>   
>> Erik Bengtson wrote:
>>     
>>> I don't think the spec prohibits multiple dbs in the backend, so my
>>> concern is to not difficult it
>>>
>>>       
>> The spec allows for multiple DBs in the backend, with a single PMF for
>> each of them (or what backend were you referring to?)
>>
>> How do you want to configure multiple database connections per PMF
>> without extending the spec?
>>     
>>> Quoting Joerg von Frantzius <joerg.von.frantzius@artnology.com>:
>>>
>>>
>>>       
>>>> 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?
>>     
>>>> Regards,
>>>> Jörg
>>>>
>>>> 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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