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From Narayanan <V.Naraya...@Sun.COM>
Subject Re: [jira] Updated: (DERBY-700) Derby does not prevent dual boot of database from different classloaders on Linux
Date Wed, 02 Aug 2006 07:53:38 GMT

Thanx a ton for the issues you have highlighted. I am sorry to have 
missed on the earlier chain of emails regarding proposal of single 
system property. I was just proposing the system property as a possible 
solution and I see the arguments against it as valid. My attempt at 
creating a rather crude simulation of the problem that can occur because 
of synchronization is attached to derby-700.

thanx once again,

Mike Matrigali wrote:
> I haven't looked at this yet, just wanted to say that when I proposed 
> a single system property (vs. one system prop per database), there was
> opposition in the community.
> Some things to think about:
> o can the same database ever have "2" names - ie. if the location is
>   /x/y/wombat and one person accesses as system=/x and db=y/wombat
> and another system= /x/y and db=wombat.
> o what about when a derby instance fails, like a null pointer or some
>   othe bug.  Will the system prop be left around?
> o how do you handle synchronization of 2 connects at basically the same
>   time?
> V.Narayanan (JIRA) wrote:
>>      [ http://issues.apache.org/jira/browse/DERBY-700?page=all ]
>> V.Narayanan updated DERBY-700:
>> ------------------------------
>>     Attachment: DERBY-700.diff
>>                 DERBY-700.stat
>> Hi,
>> We could solve this problem by setting a System property before 
>> booting a database and checking for the property during subsequent 
>> boots. When the database is shutdown we set the property to false. 
>> For example when we boot a database named mydb then we set the 
>> property derby.dblock.mydb = true. Now during subsequent boots we 
>> could check for this system variable and if it is set to true throw 
>> an exception. During the shutdown of the database we set this 
>> variable to false. I tried an attempt along this line in the attached 
>> patch.
>> I HAVE NOT run the patch with security manager enabled. The sample 
>> repro attached with this issue passes with this fix.
>> Pls note that the patch is not for a commit but is just to represent 
>> what I have in mind as a solution, in the form of code.
>> thanx
>> Narayanan
>>> Derby does not prevent dual boot of database from different 
>>> classloaders on Linux
>>> ---------------------------------------------------------------------------------

>>>                Key: DERBY-700
>>>                URL: http://issues.apache.org/jira/browse/DERBY-700
>>>            Project: Derby
>>>         Issue Type: Bug
>>>         Components: Store
>>>   Affects Versions:
>>>        Environment: ava -version
>>> java version "1.4.2_08"
>>> Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_08-b03)
>>> Java HotSpot(TM) Client VM (build 1.4.2_08-b03, mixed mode)
>>>           Reporter: Kathey Marsden
>>>        Assigned To: V.Narayanan
>>>           Priority: Critical
>>>            Fix For:
>>>        Attachments: DERBY-700.diff, DERBY-700.stat, 
>>> DualBootRepro.java, DualBootRepro2.zip
>>> Derby does not prevent dual boot from two different classloaders on 
>>> Linux.
>>> To reproduce run the  program DualBootRepro with no derby jars in 
>>> your classpath. The program assumes derby.jar is in 
>>>, you can change the location by changing the 
>>> DERBY_LIB_DIR variable.
>>> On Linux the output is:
>>> $java -cp . DualBootRepro
>>> Loading derby from file:
>>> Booted database in loader java.net.URLClassLoader@8ed465
>>> FAIL: Booted database in 2nd loader java.net.URLClassLoader@dc6a77
>>> On Windows I get the expected output.
>>> $ java -cp . DualBootRepro
>>> Loading derby from file:
>>> Booted database in loader java.net.URLClassLoader@1ac04e8
>>> PASS: Expected exception for dualboot:Another instance of Derby may 
>>> have already booted the database D:\marsden\repro\dualboot\mydb.

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