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Multiple Instance of App server- threading issue

 
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The application architecture - We have 2 application server(NOn clustered environment) with the same application , both the application server pointing to the single database.

Service : we have service which reads the database and check for the entity and if that entity is not present its adds it to the database and if it is present it will update the entity.

Problem : we have multiple threads running simultaneously to through the 2 application server. Both at the same time reads the Database and find that the entity is not present. Both thread adds the same entity in the Database. and we have duplicate rows.

The primary key and entity are different so the database doesn't restrict the duplicate rows.

Ques :
By making code thread safe by using synchronized, will it prevent the above problem ? I doubt that as we have 2 application server running on different JVM. How to prevent the above problem ? thanks in advance
 
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Please use real words when posting to the forums. Abbreviations such as "Ques" in place of "Question" only serve to make your posts more difficult to read and less likely to generate useful responses.

Please read this for more information.

thanks,
bear
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You might want to get the lock on the database object while updating so that the other server will not update.
But, this may not be a best practice.

Synchronization would help if it were in a single server. In multiple server environment, this will not work.
 
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Pass the lookup/update task objects to a single application that can coordinate access and return a result for ANY number of applications that need the function. Only this application needs to know anything about the database or whatever lies behind the function.

Possible techniques include JavaSpaces, JMS, roll your own.

Bill
 
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The primary key and entity are different so the database doesn't restrict the duplicate rows.


Of course they are different: the PK uniquely identifies the entity. Why do you have duplicate PKs? And why can't the database handle all concurrency control and deadlock detection for each transaction?
 
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