Question

I install the latest version of cplex, and use it via its JAVA API.
To avoid the overhead of constructing cplex instance, I use cplex.clearmodel and then create the new model.

But when I use it to do linear programming thousands of times, the memory leak issue is very serious. It consumed more than 2GB RAM.
Does there exist any solution to alleviate the memory leak issue?

Answer 1

I’ve encountered this issue before when running my linear programs. You must CREATE exactly one object and continue to use only one reference to that object.

import ilog.concert.*; 
import ilog.cplex.*; 
static public class Application { 
    static public main(String[] args) { 
       try {
         IloCplex cplex = new IloCplex(); 
         // create model and solve it 
       } catch (IloException e) { 
          System.err.println("Concert exception caught: " + e); 
       }
     }
   }

This issue is

IloCplex cplex = new IloCplex(); 

Only call the above line once in your program. If the clearModel method isn’t working, clear all your constraints, clear your objective function, and clear your cuts individually and then reset your constraints and objective function, but do not create a new object. That is what is causing the memory leak. To solve your new model, use

cplex.solve()

I imagine your code looks something like this

import ilog.concert.*; 
import ilog.cplex.*; 
public class Example { 
public static void main(String[] args) { 
    try { 
      for(int i = 1;i <= 5;i++){ // Loop with indices that you may use to create your constraints and objective function.
      IloCplex cplex = new IloCplex(); // Cause of memory leak
      double[]    lb = {0.0, 0.0, 0.0}; 
      double[]    ub = {40.0, Double.MAX_VALUE, Double.MAX_VALUE}; 
      IloNumVar[] x  = cplex.numVarArray(3, lb, ub); 
      double[] objvals = {1.0, 2.0, 3.0}; 
       cplex.addMaximize(cplex.scalProd(x, objvals)); 
      cplex.addLe(cplex.sum(cplex.prod(-1.0, x[0]), 
                            cplex.prod( 1.0, x[1]), 
                            cplex.prod( 1.0, x[2])), 20.0); 
      cplex.addLe(cplex.sum(cplex.prod( 1.0, x[0]), 
                            cplex.prod(-3.0, x[1]), 
                            cplex.prod( 1.0, x[2])), 30.0); 
      if ( cplex.solve() ) { 
        cplex.out().println("Solution status = " + cplex.getStatus()); 
        cplex.out().println("Solution value  = " + cplex.getObjValue());
        double[] val = cplex.getValues(x); 
        int ncols = cplex.getNcols(); 
        for (int j = 0; j < ncols; ++j) 
           cplex.out().println("Column: " + j + " Value = " + val[j]); 
      }
      cplex.end(); 
    }
    }
    catch (IloException e) { 
System.err.println("Concert exception '" + e + "' caught"); 
    }
  }
}

Start your for or while loops after you create your instance of the IloCplex object. So, in contrast to the code above, do

IloCplex cplex = new IloCplex(); // Cause of memory leak
for(int i = 1;i <= 5;i++){ // Loop with indices that you may use to create your constraints and objective function.