2 Replies Latest reply on May 30, 2011 11:34 PM by 865172

    Multi thread issue.

      I have been working on a project and would be grateful if i get a solution for this. The issue i am facing is when two admin update the details of a " same user " simultaneously there is occurrence of duplicate rows in the table. Here i use KODO framework to delete and insert new values in table whenever admin clicks save button. (here update is complex , so delete and insert is used).

      so when two admin clicks save button simultaneously the duplicate rows occur in table.

      how can i fix this issue, i think using synchronize is a bad option as it eats up performance.
      Is there a way to fix this multi threading issue in java without locking up or holding up resources(such that performance of application does not decrease) , since this a commonly used part of my web application ?.
        • 1. Re: Multi thread issue.
          The normal way to avoid this issue would be to have a unique index on the table which prevents duplicate entries.

          I wouldn't delete the entry, only insert the entry if it doesn't exist and update it if it does.

          If you lock on a key unique to the user/row (rather than the whole table) your overhead will be about 2 micro-seconds. This is extremely small for an application driven by user interaction. You could lock the whole table which might limit your application to about 100 updates per second but would be much simpler to manage. Personally, if admins are performing more than 100 updates per second there is something wrong with your model.

          In short I would just lock the whole table and optimise it if this proved to be an issue.
          • 2. Re: Multi thread issue.
            I'm agree with Peter, use primary keys or secondary unique keys that identify data in your tables (if you can't, you have a database design problem) and then lock the rows affected in the Admin operation at row level. It only locks operations on the same rows until commit/rollback is done, so application's performance is only affected for the second Admin attended for milliseconds if they aren't long ops. It's thread safe and cluster safe.
            You probably must think to redefine the Admin operations if they're critical in your application.
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