1. A load balancing method for multi-tenant database system, load balancing method comprising: a. generating a replica swap operator to achieve a load transfer with minimal service interruption; b. determining an optimal set of swap operators that minimizes a total cost; and c. sequencing swap operators to minimize or avoid temporary overloads; wherein the sequencing includes swap operators SW i , 1≦i≦N sw and servers S sink involved in SW i , 1≦i≦Ns and outputs a swap sequence for j←1 to N s where if Si has no outgoing edge swap then S j is added to the set S sink , and while S sink ≈0 an incoming edge swap SW i is picked and appended to the swap sequence, SW i is removed from its destination server Sj and the source server S j2 , if S j has no incoming edge it is removed from Ssink and if S j2 has no outgoing edge, it is added to S sink .