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Hibernate loses precision when persisting util.Date as timestamp

 
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I find it happening randomly and much more often than not.
I have a simple Hibernate mapped object that has a util.Date as one of the properties.
I set this Date whenever I create the object and then just persist it using Hibernate.
The target property in the SQL Server 2000 DB is of type datetime. After the inserts, I can compare the inserted values from my logs to find that hibernate in general add 2 millisecond to every date it inserts!!
I do not find any related posting on the net so far.

The piece of relevant code is :



With this code, some values I could observe where like this :

  • utilTime =1163605588780 persistedTime=1163605588780
  • utilTime =1163605624045 persistedTime=1163605624047
  • utilTime =1163605651029 persistedTime=1163605651030
  • utilTime =1163605675544 persistedTime=1163605675543
  • utilTime =1163605703216 persistedTime=1163605703217
  • utilTime =1163605731418 persistedTime=1163605731417




  • I find the bartenders around here are quite seasoned to point out anything I might be doing wrong, before I finally signup for Hibernate forums and post this as bug there.
    Thanks for giving it a look and hopefully thought too.
     
    Bartender
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    Is this your complete test case? I don't see where you log persistedTime.
     
    Manzar Zaidi
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    Thanks for your reply Paul.
    no, this is not even the test case.
    but I do nothing at all other than what I have there.
    I set a date value in an object property mapped to a SQL Server Datetime column and save the object.
    I realize that if you guys have not observed this anywhere else and dont see any obvious mistake I might be doing, I have to explicitly test this thing and check the possibility of a bug in Hibernate/JDK5/jtds driver.
    Thats something I will do as soon as I get to my workstation tomorrow.
     
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    You should realize that what you are saying is "I ran code A, and I thought there was something wrong with its output, so here's code B which, trust me, is similar." It would be better if you showed us the actual test code that produces that output.
     
    Manzar Zaidi
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    I am sorry, I think I did not communicate well enough.
    The code I posted is the code that produces the issue. I have a JUnit class testing this piece out, but thats too domain specific to make any point here.
    I hoped to get any 'I have seen it'/'You are doing that things again' kind of comments before I actually Isolated a test for what appears to be the issue.
    I think I will be back with the isolated test soon. Have a good day ahead.
    [ November 15, 2006: Message edited by: Manzar Zaidi ]
     
    ranger
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    Maybe it is just a databsae thing. Meaning how the database stores timestamps changes the Timestamp by a small bit.

    Mark
     
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    Hi Manzar,

    Mark is right here. If you search on SQL Server and timestamps, you 'll find that these are not as precise as you 'd like. I am not sure about the exact magnitude, but I think it may be off by one third of a second. More detail can be found in the SQL Server docs, or on the internet.

    Regards,

    Rudy.
     
    Paul Sturrock
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    Originally posted by Rudy Dakota:
    Hi Manzar,

    Mark is right here. If you search on SQL Server and timestamps, you 'll find that these are not as precise as you 'd like. I am not sure about the exact magnitude, but I think it may be off by one third of a second. More detail can be found in the SQL Server docs, or on the internet.

    Regards,

    Rudy.




    Do you mean datetime data types? A timestamp is a different thing in SQL Server from an SQL timestamp - it is only really used as a versioning field. SQL Server uses datetime to represent dates instead. It is true that SQL Server datetimes do only have 3 digits of fractoral precision (where Oracle has 9), but are documented to be accurate to within 3.33 miliseconds (or c1/333 of a second). I would be suprised if this added up to a difference of 2 milliseconds in a normal calculation though; if this has been happening in SQL Server I've never noticed it before.

    Though this is by no means conclusive Manzar Zaidi, I work with both Hibernate 2* and 3*, and SQL SQerver 2000 and 2005, and have yet to notice it. Though this may just be because any time calculations we use don't require the same level of precision.
     
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