Are Deadlocks inevitable ?

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  • John Rivers
    #1

    Are Deadlocks inevitable ?

    There are many references to deadlock handlers that retry the
    transaction automatically.

    But IMO a deadlock is the result of a design flaw that should be
    fixed.

    My applications treat deadlocks like any other runtime error - they
    are logged and fixed.

    There seems to be a an opinion that deadlocks are inevitable !

    This is not true - any scenario resulting in a deadlock can be cured
    by adjusting the application.

    I have talked with database consultants working for banks that think
    deadlocks are an acceptable every day occurrence.

    Now that is scary ...

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    • Serge Rielau
      #2
      Re: Are Deadlocks inevitable ?

      John Rivers wrote:
      There are many references to deadlock handlers that retry the
      transaction automatically.
      >
      But IMO a deadlock is the result of a design flaw that should be
      fixed.
      >
      My applications treat deadlocks like any other runtime error - they
      are logged and fixed.
      >
      There seems to be a an opinion that deadlocks are inevitable !
      >
      This is not true - any scenario resulting in a deadlock can be cured
      by adjusting the application.
      I wouldn't go as far as claiming "any".
      I have talked with database consultants working for banks that think
      deadlocks are an acceptable every day occurrence.
      If you have a complex transaction with many concurrent users I think I
      agree that deadlocks are inevitable.
      You cannot realistically sort data access/change in a way to always
      guarantee lock waits over deadlocks at a reasonable expense.
      So fault toleration is the more sensible way.

      Cheers
      Serge
      --
      Serge Rielau
      DB2 Solutions Development
      IBM Toronto Lab

        Comment

        • Serge Rielau
          #3
          Re: Are Deadlocks inevitable ?

          Serge Rielau wrote:
          John Rivers wrote:
          >There are many references to deadlock handlers that retry the
          >transaction automatically.
          >>
          >But IMO a deadlock is the result of a design flaw that should be
          >fixed.
          >>
          >My applications treat deadlocks like any other runtime error - they
          >are logged and fixed.
          >>
          >There seems to be a an opinion that deadlocks are inevitable !
          >>
          >This is not true - any scenario resulting in a deadlock can be cured
          >by adjusting the application.
          I wouldn't go as far as claiming "any".
          >
          >I have talked with database consultants working for banks that think
          >deadlocks are an acceptable every day occurrence.
          >
          If you have a complex transaction with many concurrent users I think I
          I meant complex _application_ ...

          --
          Serge Rielau
          DB2 Solutions Development
          IBM Toronto Lab

            Comment

            • John Rivers
              #4
              Re: Are Deadlocks inevitable ?


              An interesting idea:

              to swap a deadlock-proof design for a higher performing design that
              suffers deadlocks

              but by accepting deadlocks you risk one client being selected as the
              deadlock victim repeatedly for a long period of time ... potentially
              forever!

                Comment

                • Erland Sommarskog
                  #5
                  Re: Are Deadlocks inevitable ?

                  John Rivers (first10@btinte rnet.com) writes:
                  but by accepting deadlocks you risk one client being selected as the
                  deadlock victim repeatedly for a long period of time ... potentially
                  forever!
                  If you have that high deadlock frequency, you better do something about it.

                  It is possible that every deadlock that occurs in an application could be
                  address. But what would the cost be? And what would the risk be that you
                  introduce bugs or performance bottlenecks.

                  If you have a bunch of background processes that deadlocks with each
                  other, or at least willing to become the deadlock victim, then some 20-30
                  deadlocks per day is not a big issue. It becomes an issue, if users get
                  this message slapped in the face 20-30 times a day, or if you have deadlocks
                  every minute. Then again, if you have deadlocks every minute, the deadlocks
                  are likely to be a symptom of a general performance problem.



                  --
                  Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

                  Books Online for SQL Server 2005 at
                  http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

                  Books Online for SQL Server 2000 at
                  http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

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