Colocate Groups

Tries moving a related set of objects that share a scope item to every possible combination of containers in each of the other scope items, so that related groups end up colocated within the same scope. Useful when several groups (e.g. the shards of a replica set) must live together in the same region or fault domain.

Parameters

Parameter	Type	Required	Default	Description
partitionName	string	Yes	-	The partition whose groups are colocated
relatedGroupsList	list<ColocateGroupsMoveTypeRelatedGroupsInfo>	Yes	-	Sets of related groups; each set is colocated together, and the sets must be disjoint
colocationScopeName	string	Yes	-	The scope within which each set of related groups must be colocated (e.g. region)
colocationScopeItemToGroupToContainers	map	No	all containers	Per scope item and group, restricts the candidate containers considered
defaultSampleSize	int	No	all destinations	Samples the candidate containers for each (group, scope item)

Behavior

For each set of related groups, the move type evaluates relocating the group's objects from their current scope item into the containers of every other scope item, trying the possible container combinations (optionally sampled). The best combination that improves the objective---bringing the related groups into the same scope---is applied.

Complexity

Roughly n * |S| * |G|^k, where n is the number of objects moved, |S| the number of scope items, |G| the candidate containers per group, and k the number of groups colocated together.

Example

Configure local search to use only the colocate groups move type:

ColocateGroupsMoveTypeSpec colocateGroups;
colocateGroups.partitionName() = "replica_set";
colocateGroups.colocationScopeName() = "region";
// relatedGroupsList describes which groups must be colocated together.

LocalSearchSolverSpec localSearch;
localSearch.moveTypeList()->push_back(
    ProblemSolver::makeMoveTypeSpec(colocateGroups));

solver.addSolver(localSearch);

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