MDTUpdate: A Multi-Block Double Tree Update Technique in Heterogeneous Erasure-Coded Clusters

A significant drawback of erasure codes is suffering from the expensive update overhead, and all parity blocks are regenerated once any update of one data block for consistency. Existing update techniques either neglect the multi-block updates scenario under update-intensive workloads or do not consider how to minimize the update cost in heterogeneous clusters. This paper presents the first systematic study on multi-block updates in heterogeneous clusters. We formulate the problem as a cost-based routing optimization model and propose a novel Multi-block Double Tree Update ( MDTUpdate ) technique. The key idea is to construct a double tree structure for multiple updated data blocks and all parity blocks, which avoids the congested link bottleneck. To reduce the update costs effectively, we exploit a hybrid update scheme that combines the data-delta and parity-delta schemes under the double tree structure. To accelerate the tree construction, we design a time-efficient greedy algorithm that timely determines the transmission route via perceiving the cost discrepancy among nodes while avoiding exhaustive enumeration. We further prove that our algorithm is optimal in minimizing the update costs. The experiments show that MDTUpdate can improve the update performance by up to 83.23% over the existing techniques while incurring extremely lightweight running overhead.