private static Result <ModelOutput> Predict(RedisClusterSize currentClusterSize, ModelContext modelContext)
{
// TODO: autoscaler should consider the server load percentage as well. If a shard had a very high load
// percentage, it means that it is for some reason receiving an uneven load. Hence, adding shards helps in
// this situation. There is no easy way to add that to the current model. Ideas:
// - If any server reached a load >70% at any time in the period analyzed, we need to guarantee that
// there's at least as many shards as there were before (i.e. no downscales are allowed).
var shortestPaths = ComputeAllowedPaths(currentClusterSize, modelContext);
var eligibleClusterSizes = shortestPaths
.Select(kvp => (Size: kvp.Key, Node: kvp.Value))
// Find all plans that we can reach from the current one via scaling operations, and that we allow scaling to
.Where(entry => entry.Node.ShortestDistanceFromSource != double.PositiveInfinity && IsScalingAllowed(currentClusterSize, entry.Size, modelContext))
// Compute the cost of taking the given route
.Select(entry => (entry.Size, entry.Node, Cost: CostFunction(currentClusterSize, entry.Size, modelContext, shortestPaths)))
.ToList();
// Rank them by cost ascending
var costSorted = eligibleClusterSizes
.OrderBy(pair => pair.Cost)
.ToList();
if (costSorted.Count == 0)
{
return(new Result <ModelOutput>(errorMessage: "No cluster size available for scaling"));
}
return(new ModelOutput(
targetClusterSize: costSorted[0].Size,
modelContext: modelContext,
cost: costSorted[0].Cost,
scalePath: RedisScalingUtilities.ComputeShortestPath(shortestPaths, currentClusterSize, costSorted[0].Size)));
}
private Result <ModelOutput> Predict(RedisClusterSize currentClusterSize, ModelContext modelContext)
{
var shortestPaths = ComputeAllowedPaths(currentClusterSize, modelContext);
var eligibleClusterSizes = shortestPaths
.Select(kvp => (Size: kvp.Key, Node: kvp.Value))
// Find all plans that we can reach from the current one via scaling operations, and that we allow scaling to
.Where(entry => entry.Node.ShortestDistanceFromSource != double.PositiveInfinity && IsScalingAllowed(currentClusterSize, entry.Size, modelContext))
// Compute the cost of taking the given route
.Select(entry => (entry.Size, entry.Node, Cost: CostFunction(currentClusterSize, entry.Size, modelContext, shortestPaths)))
.ToList();
// Rank them by cost ascending
var costSorted = eligibleClusterSizes
.OrderBy(pair => pair.Cost)
.ToList();
if (costSorted.Count == 0)
{
return(new Result <ModelOutput>(errorMessage: "No cluster size available for scaling"));
}
return(new ModelOutput(
targetClusterSize: costSorted[0].Size,
modelContext: modelContext,
cost: costSorted[0].Cost,
scalePath: RedisScalingUtilities.ComputeShortestPath(shortestPaths, currentClusterSize, costSorted[0].Size)));
}
public void FailsOnNonExistantRoute()
{
var from = RedisClusterSize.Parse("P1/1");
var to = RedisClusterSize.Parse("P3/3");
var path = RedisScalingUtilities.ComputeShortestPath(from, to, size => new RedisClusterSize[] { }, (f, t) => 1);
path.Should().BeEmpty();
}
public void SucceedsOnSimpleRoute()
{
var from = RedisClusterSize.Parse("P1/1");
var to = RedisClusterSize.Parse("P3/3");
var path = RedisScalingUtilities.ComputeShortestPath(from, to, size => size.ScaleEligibleSizes, (f, t) => 1);
path.Should().BeEquivalentTo(new RedisClusterSize[] { RedisClusterSize.Parse("P3/1"), RedisClusterSize.Parse("P3/3") });
}
public void CanFindEmptyRoute()
{
var from = RedisClusterSize.Parse("P1/1");
var to = RedisClusterSize.Parse("P1/1");
var path = RedisScalingUtilities.ComputeShortestPath(from, to, size => size.ScaleEligibleSizes, (f, t) => 1);
path.Should().BeEmpty();
}
public void CanFindSingleRoute()
{
var from = RedisClusterSize.Parse("P1/1");
var to = RedisClusterSize.Parse("P1/2");
var path = RedisScalingUtilities.ComputeShortestPath(from, to, size => size.ScaleEligibleSizes, (f, t) => 1);
path.Count.Should().Be(1);
path[0].Should().Be(to);
}
/// <summary>
/// This function embodies the concept of "how much does it cost to switch from
/// <paramref name="current"/> to <paramref name="target"/>". At this point, we can assume that:
/// - The two input sizes are valid states to be in
/// - We can reach the target from current via some amount of autoscaling operations
/// Hence, we're just ranking amonst the many potential states.
/// </summary>
private static double CostFunction(RedisClusterSize current, RedisClusterSize target, ModelContext modelContext, IReadOnlyDictionary <RedisClusterSize, RedisScalingUtilities.Node> shortestPaths)
{
// Switching to the same size (i.e. no op) is free
if (current.Equals(target))
{
return(0);
}
var shortestPath = RedisScalingUtilities.ComputeShortestPath(shortestPaths, current, target);
Contract.Assert(shortestPath.Count > 0);
// Positive if we are spending more money, negative if we are saving
return((double)(target.MonthlyCostUsd - current.MonthlyCostUsd));
}