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Whole solving time spent on Sync [CPLEX]

  • 1.  Whole solving time spent on Sync [CPLEX]

    Posted 04/26/16 10:59 AM

    Originally posted by: cesnjak


    Hello,

     

    I am running relatevily large MIP problems consisting of 1736581 rows, 1502775 columns, and 9622430 nonzeros, 21361 binaries, 96 generals, 0 SOSs, and 0 indicators.

     

    I have encountered a problem recently. This is copy/paste from log file:

     

    Root relaxation solution time = 3613.18 sec. (2991145.84 ticks)

            Nodes                                         Cuts/
       Node  Left     Objective  IInf  Best Integer    Best Bound    ItCnt     Gap

          0     0  3739923.9305  2766                3739923.9305       35         
          0     0  3739925.2353  2793                 Cuts: 10000    22999         
          0     0  3739976.7930  2794                  Cuts: 9999    44474         
    Heuristic still looking.
    Heuristic still looking.
    Heuristic still looking.
    Heuristic still looking.
          0     2  3739976.7930  2794                3741595.4806    44474         
    Elapsed time = 97136.42 sec. (36702808.00 ticks, tree = 0.00 MB, solutions = 0)

    Flow cuts applied:  150
    Mixed integer rounding cuts applied:  19620
    Gomory fractional cuts applied:  6

    Root node processing (before b&c):
      Real time             = 97121.53 sec. (36692136.30 ticks)
    Parallel b&c, 8 threads:
      Real time             = 902882.90 sec. (131455209.12 ticks)
      Sync time (average)   = 790018.39 sec.
      Wait time (average)   =    0.00 sec.
                              ------------
    Total (root+branch&cut) = 1000004.43 sec. (168147345.42 ticks)


    MIP - Time limit exceeded, no integer solution.
    Current MIP best bound =  3.7415954806e+06 (gap is infinite)
    Solution time = 1000004.44 sec.  Iterations = 9842732  Nodes = 1 (2)
    Deterministic time = 168147351.18 ticks  (168.15 ticks/sec)


    CPLEX Error  3020: No MIP start exists.
    No file written.

    CPLEX Error  1217: No solution exists.
    No file written.

     

    Basically the problem is once branching starts, the remaining time is spent on sync. I have no clue why is this happening. And I have been running same problem with some different parameters on the same machine with no such problem so it is not to some specific local machine hardware/software problem.

     

    These are the cplex parameters I am using:

    CPX_PARAM_EPGAP    0.05
    CPX_PARAM_THREADS 8
    CPX_PARAM_TILIM 1000000
    CPX_PARAM_WORKMEM 23500
    CPX_PARAM_NODEFILEIND 3
    CPX_PARAM_PARALLELMODE -1
    CPX_PARAM_MIPDISPLAY 4
    CPX_PARAM_MIPEMPHASIS 0
    CPX_PARAM_EPRHS 1e-05

     

    Do you know what is the reason and how can I solve this?

    Thank you!

     

    P.S. I am not sure which information do I need to provide. So if you need some additional data, please say.


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    #DecisionOptimization


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