Originally posted by: martin#r

Hi,

I experience a strange delay during my cplex runs when branch&bound starts. I experienced it in cplex 12.5 and 12.6. My formulation uses a lazy and a user-cutcallback. I added prints to this callback at the start and end. Then I get the following output:

      1     3      361.9702  1359                    357.1675    57581                     y_10 N      1      0      1
<strange delay>
START_user
END_user
START_user
END_user
START_user
END_user
START_user
END_user
      2     4      389.7698  1054                    361.9706    74578                     y_10 N      2      0      1
<strange delay>
START_user
END_user
START_user
END_user
      3     5      363.1496  1393                    362.0136    82511                     y_59 D      3      1      2

There is a slight delay between 'END' and the cplex output. This one should be the LP-resolve. But then there is second delay between the cplex-output and the next 'START'. This delay is sometimes multiple seconds long and I do not know the reason for it.

If anyone has ideas what this might be or ideas on some additional ouput I might submit your help is highly appreciated.

I already disabled a few things (all defines are currently enabled):

cplex->setParam( IloCplex::Threads, 1);

#if defined(CPLEX_CUTS_OFF) || defined(LP_BOUND)
        cplex->setParam( IloCplex::FlowCovers, -1);
                cplex->setParam( IloCplex::FlowPaths, -1);
                cplex->setParam( IloCplex::MIRCuts, -1);     //disable mixed integer rounding cuts
                cplex->setParam( IloCplex::FracCuts, -1);    //disable Gomory fractional cuts
                cplex->setParam( IloCplex::ImplBd, -1);              //disable implied bound cuts
                //cplex->setParam( IloCplex::LiftProjCuts, -1);      //only relevant for cplex 12.6
                cplex->setParam( IloCplex::EachCutLim, 0);
#endif

#if defined(CPLEX_HEURISTICS_OFF) || defined(LP_BOUND)
                cplex->setParam( IloCplex::HeurFreq, -1);
                cplex->setParam( IloCplex::RINSHeur, -1);
                cplex->setParam( IloCplex::FPHeur, -1);
#endif

#if defined(CPLEX_PRESOLVING_OFF) || defined(LP_BOUND)
                cplex->setParam( IloCplex::PreInd, false);
                cplex->setParam( IloCplex::RelaxPreInd, 0);
                cplex->setParam( IloCplex::RepeatPresolve, 0);
                cplex->setParam( IloCplex::PreslvNd, -1);
                cplex->setParam( IloCplex::Probe, -1);
                cplex->setParam( IloCplex::ProbeTime, 1e+75);
#endif

Very hard to tell what may be going on. Is there any chance you can run a profiler on your code to get an idea where the time is spent?