Xpress Optimizer Memory Issue and Configuration

In order to correctly handle memory in C# BCL, make sure you Dispose() as soon as possible of any BCL objects that implement the IDisposable interface. For example, wrap them in a "using" block.

You may also want to use the XPRBexprContext class to make sure you get rid of XPRBexpr instances, which may otherwise a bit hard to assert.

In general, no special code should be required when running on Linux.

You may also want to switch to a more recent version of Xpress since some things about memory management improved in the last releases.

Finally, in version 9.4 a new C# API was introduced that is similar but more flexible than BCL. It also has a smaller memory footprint than BCL. You can find the details about this here.

Hi @Daniel Junglas​ ,

Thank you for the reply. I want to confirm if we are disposing of all Xpress entities correctly.

In our algorithm, we are solving multiple MIP models iteratively. For each step following is the way we use Xpress.

1. We have an object XpressSolver which implements IDisposable.
2. We initialize the OEM license in the constructor that does
   1. XPRB.init() and XPRS.License()

• Using XpressSolver we create an object called XpressModel like below

using (XPRBexprContext ctx = new XPRBexprContext())
{
    var bclProblem = new XPRBprob(problemName);
    var optimizerProblem = bclProblem.getXPRSprob();
 
    return new XpressModel(problemName, bclProblem, optimizerProblem, new XpressParameterData(optimizerProblem), this.logger);
}

• Xpress model is also Disposable.
• We solve the model (creating variables, expressions, constraints etc.)
• Once the model is done we dispose bclProblem and optimizerProblem.
• Then we dispose the XpressSolver to release the license by calling
  • XPRB.free()

Based on your answer It seems we are not using XPRBexprContext correctly. I believe we should create that object and keep it in the model and dispose of it when the model is done.

Please let me know if that understanding is correct. Also, do we need to dispose of any other Xpress objects like variables or constraints, etc.?

Best,

Shamsher

Yes, your understanding is correct: The lifetime of XPRSexprContext should be the same as XPRBprob.

There is no need to dispose of XPRBvar or XPRBctr, these are cleanup up automatically (in fact, they don't inherit from IDisposable, so you cannot even call Dispose() on them). The only other things that requires disposal is XPRBbasis in case you use that.