// Moves a single partition from the largest entry to the smallest. only
// if the smallest entry is smaller then the rest.
// if all entries are the same size, then a random entry is chosen
func RebalanceSingle(services *Services, routerTable *shards.RouterTable) error {
var smallest *shards.RouterEntry = nil
var largest *shards.RouterEntry = nil
min := int(routerTable.TotalPartitions / len(routerTable.Entries))
services.Logger.Printf("Looking for entries with more then %d partitions", min)
//shuffle the entries array
entries := make([]*shards.RouterEntry, len(routerTable.Entries))
perm := rand.Perm(len(routerTable.Entries))
for i, v := range perm {
entries[v] = routerTable.Entries[i]
}
for _, entry := range entries {
if len(entry.Partitions) < min {
if smallest == nil {
smallest = entry
} else if len(entry.Partitions) < len(smallest.Partitions) {
smallest = entry
}
if largest == nil {
largest = entry
} else if len(entry.Partitions) > len(largest.Partitions) {
largest = entry
}
}
}
if smallest == nil || largest == nil {
services.Logger.Printf("Cluster appears to be balanced")
return nil
}
services.Logger.Printf("Moving from %s to %s", largest.Id(), smallest.Id())
return nil
}
