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AvoidMoving

Type: Constraint

Pin a set of objects to the containers they start in, so Rebalancer never moves them. For example, hold a few tasks in place while it rebalances everything else.

Parameters​

ParameterTypeRequiredDefaultDescription
namestringNo""Descriptive name for logging/debugging.
objectslist of stringYesemptyThe objects pinned to their initial container.

Example​

An example use: three tasks start on host0, and an AssignmentAffinitiesSpec goal makes task0 and task1 prefer host1. Pinning task0 keeps it on host0, so only task1 moves.

solver.setObjectName("task");
solver.setContainerName("host");

solver.setAssignment(std::map<std::string, std::vector<std::string>>{
    {"host0", {"task0", "task1", "task2"}},
    {"host1", {}},
});

// task0 and task1 prefer host1 (an AssignmentAffinitiesSpec goal).
auto pref = [](std::string task, std::string host, double affinity) {
  AssignmentAffinity entry;
  entry.objectName() = std::move(task);
  entry.scopeItemName() = std::move(host);
  entry.affinity() = affinity;
  return entry;
};
AssignmentAffinitiesSpec prefersHost1;
prefersHost1.scope() = "host";
prefersHost1.affinities() = {pref("task0", "host1", 1), pref("task1", "host1", 1)};
solver.addGoal(prefersHost1);

// Pin task0 to its initial container.
AvoidMovingSpec avoidMovingSpec;
avoidMovingSpec.objects() = {"task0"};
solver.addConstraint(avoidMovingSpec);

task1 moves to its preferred host1. task0 would prefer host1 too but is pinned, so it stays on host0. task2 has no reason to move.

Constraint only​

AvoidMovingSpec cannot be used as a goal; passing it to addGoal throws.

It keeps each listed object in the container it starts in. The initial assignment already satisfies this (nothing has moved yet), so the constraint is never broken and these objects never move.

If an object is also named in a MovesInProgressSpec (a forced move), the forced move takes precedence and the object may move.

Source​