Shigero Sasaki

Analytical model of inter-node communication under multi-versioned coherence mechanisms

Our goal is to predict the performance of multi-node systems consisting of identical processing nodes based on single node profiles. The performance of multi-node systems significantly depends on the amount of inter-node communication. Therefore, we built an analytical model of the communication amount, i.e., the number of transfers of cached copies, on multi-node systems with coherence mechanisms that support multi-versioning. Multi-versioned mechanisms are assumed because databases are most likely to be the bottleneck and because a typical clustered database has one of these mechanisms. In our model, the number of transfers of copies of a block per write access is expressed as a function of a write ratio, the number of nodes, and the lock down factor which denotes how many versions of copies can exist. To empirically verify our analytical and theoretical model, we compared the number of transfers that predicted by our model and that counted by a toy simulator of multi-versioned mechanisms.

An analytical model of inter-node communication towards performance prediction of multi-node systems

Our goal is to predict the performance of multi-node systems consisting of identical processing nodes based on single node profiles. We clarified how much inter-node communication is caused on n-node systems because the performance significantly depends on the communication amount. However, the amount when business applications such as databases are running is difficult to predict for the following reasons: first, applications are closed and/or complex. Second, workloads vary from system to system. Third, the number of nodes affects the amount. We analytically model the amount under a simple cache coherence mechanism. Our model predicted, with a high degree of accuracy, the number of transfers of cached copies obtained by simulation. Even though our model explains the transfers only under a simple mechanism, the model should explain a fundamental part of those under more complex ones.

Modelling coherence overhead of multi-versioned caches for random accesses

Our goal is to predict the performance of multi-node systems consisting of identical processing nodes from single node profiles. The performance of multi-node systems that have coherent caches considerably depends on coherence overhead, which is roughly in direct proportion to the number of transfers of cached copies. We analytically model the number of transfers of cached copies of a data block per write access for random accesses where multi-node systems have multi-versioned coherence mechanisms. Our model aims at helping to predict a baseline performance when closed and/or complex business applications are running, such as clustered databases, the algorithmic behaviours of which are practically impossible to analyse and characteristics of which vary from system to system. To empirically verify our analytical model and show how coherence overhead varies in accordance with parameters, we compared the number of transfers that was predicted by our model and that was counted by a toy simulator of multi-versioned mechanisms.