I have a general question about the branch and bound performance when operated on >1 cores.
I recently ran a rather large optimization problem (100000+ decision variables, 1000+ integers) on 30 threads. What struck me about the computation time was how it developed over the solution process. The root relaxation solved in 16 hours, 3 nodes in 63 hours and 7 nodes in 139 hours. If you break this down, you get a more or less constant calculation time of about 20 hours per node.
Now, I know that this is a very simplified analysis since every node poses a slightly different problem, but still I would expect the calculation time per node to go down with increasing number of nodes due to the parallelization. From my simplified analysis, I would conclude that the nodes are solved sequentially, not parallel.
My question is now if I'm missing something here or if you would draw the same conclusion?
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