Section: New Results

Efficient data management for hybrid and multi-site clouds

JetStream: enabling high-throughput live event streaming on multi-site clouds

Participants : Radu Tudoran, Alexandru Costan, Gabriel Antoniu.

Scientific and commercial applications operate nowadays on tens of cloud datacenters around the globe, following similar patterns: they aggregate monitoring or sensor data, assess the QoS or run global data mining queries based on inter-site event stream processing. Enabling fast data transfers across geographically distributed sites allows such applications to manage the continuous streams of events in real time and quickly react to changes. However, traditional event processing engines often consider data resources as second-class citizens and support access to data only as a side-effect of computation (i.e. they are not concerned by the transfer of events from their source to the processing site). This is an efficient approach as long as the processing is executed in a single cluster where nodes are interconnected by low latency networks. In a distributed environment, consisting of multiple datacenters, with orders of magnitude differences in capabilities and connected by a WAN, this will undoubtedly lead to significant latency and performance variations.

This is namely the challenge we addressed this year by proposing JetStream [15] , a high performance batch-based streaming middleware for efficient transfers of events between cloud datacenters. JetStream is able to self-adapt to the streaming conditions by modeling and monitoring a set of context parameters. It further aggregates the available bandwidth by enabling multi-route streaming across cloud sites, while at the same time optimizing resource utilization and increasing cost efficiency. The prototype was validated on tens of nodes from US and Europe datacenters of the Windows Azure cloud with synthetic benchmarks and a real-life application monitoring the ALICE experiment at CERN. The results show a $3\times$ increase of the transfer rate using the adaptive multi-route streaming, compared to state of the art solutions.

Multi-site metadata management for geographically distributed cloud workflows

Participants : Luis Eduardo Pineda Morales, Alexandru Costan, Gabriel Antoniu.

With their globally distributed datacenters, clouds now provide an opportunity to run complex large-scale applications on dynamically provisioned, networked and federated infrastructures. However, there is a lack of tools supporting data-intensive applications (e.g. scientific workflows) on virtualized IaaS or PaaS systems across geographically distributed sites. As a relevant example, data-intensive scientific workflows struggle in leveraging such distributed cloud platforms. For instance, scientific workflows which handle many small files can easily saturate state-of-the-art distributed filesystems based on centralized metadata servers (e.g., HDFS, PVFS).

In [22] , we explore several alternative design strategies to efficiently support the execution of existing workflow engines across multi-site clouds, by reducing the cost of metadata operations. These strategies leverage workflow semantics in a 2-level metadata partitioning hierarchy that combines distribution and replication. The system was validated on the Microsoft Azure cloud across 4 EU and US datacenters. The experiments were conducted on 128 nodes using synthetic benchmarks and real-life applications. We observe as much as 28% gain in execution time for a parallel, geo-distributed real-world application (Montage) and up to 50% for a metadata-intensive synthetic benchmark, compared to a baseline centralized configuration.

Understanding the performance of Big Data platforms in hybrid and multi-site clouds

Participants : Roxana-Ioana Roman, Ovidiu-Cristian Marcu, Alexandru Costan, Gabriel Antoniu.

Recently, hybrid multi-site big data analytics (that combines on-premise with off-premise resources) has gained increasing popularity as a tool to process large amounts of data on-demand, without additional capital investment to increase the size of a single datacenter. However, making the most out of hybrid setups for big data analytics is challenging because on-premise resources can communicate with off-premise resources at significantly lower throughput and higher latency. Understanding the impact of this aspect is not trivial, especially in the context of modern big data analytics frameworks that introduce complex communication patterns and are optimized to overlap communication with computation in order to hide data transfer latencies. This year we started to work on a study that aims to identify and explain this impact in relationship to the known behavior on a single cloud.

A first step towards this goal consisted of analysing a representative big data workload on a hybrid Spark setup [24] . Unlike previous experience that emphasized low end-impact of network communications in Spark, we found significant overhead in the shuffle phase when the bandwidth between the on-premise and off-premise resources is sufficiently small. We plan to continue this study by investigating additional parameters at a finer grain and adding new platforms, like Apache Flink.