Comparison of eager and quorum-based replication in a cloud environment

Abstract

Most applications deployed in a Cloud require a high degree of availability. For the data layer, this means that data have to be replicated either within a data center or across Cloud data centers. While replication also allows to increase the performance of applications if data is read as the load can be distributed across replica sites, updates need special coordination among the sites and may have an adverse effect on the overall performance. The actual effects of data replication depend on the replication protocol used. While ROWAA (readone-write-all-available) prefers read operations, quorum-based replication protocols tend to prefer write operations as not all replica sites need to be updated synchronously. In this paper, we provide a detailed evaluation of ROWAA and quorum-based replication protocols in an amazon AWS Cloud environment on the basis of the TPC-C benchmark and different transaction mixes. The evaluation results for single data center and multi data center environments show that in general the influence of transaction coordination significantly grows with the number of update sites and a growing number of update transactions. However, not all quorum-based protocols are well suited for high update loads as they may create a hot spot that again significantly impacts performance.

QuAD: A quorum protocol for adaptive data management in the cloud

“…QuAD considers the load of the sites and their distance, i.e., the round-trip time (RTT), when determining the quorums. Additionally, QuAD seeks a possibly balanced assignment of sites to quorums, since if sites are frequently included in the quorums, they may become a bottleneck [13].…”

“…The balancing penalty (balP en, Eq. (4) and (7)) is used to increase the cost of Q with increasing number of slaves assigned to Q, and it fulfills the purpose of a balanced assignment of the slaves to core sites, as otherwise they may become a bottleneck [13]. #SL(Q) in Eq.…”