arXiv subjects

Foivos Zakkak

Publications and source records attributed to Foivos Zakkak.

2 recordsLinked to original sources

arXiv2023

Garbage Collection or Serialization? Between a Rock and a Hard Place!

Big data analytics frameworks, such as Spark and Giraph, need to process and cache massive amounts of data that do not always fit on the heap. Therefore, frameworks temporarily move long-lived objects outside the managed heap (off-heap) on a fast storage device. Unfortunately, this practice results in: (1) high serialization/deserialization (S/D) cost, and (2) high memory pressure when off-heap objects are moved back to the managed heap for processing. In this paper, we propose TeraHeap, a system that eliminates S/D overhead and expensive GC scans for a large portion of the objects in big data frameworks. TeraHeap relies on three concepts. (1) It eliminates S/D cost by extending the managed runtime (JVM) to use a second high-capacity heap (H2) over a fast storage device. (2) It reduces GC cost by fencing the garbage collector from scanning H2 objects. (3) It offers a simple hint-based interface, which allows frameworks to leverage knowledge about objects for populating H2. We implement TeraHeap in OpenJDK and evaluate it with 15 widely used applications in two real-world big data frameworks, Spark and Giraph. Our evaluation shows that for the same DRAM size, TeraHeap improves performance by up to 73% and 28% compared to native Spark and Giraph, respectively. Also, it provides better performance by consuming up to 8x and 1.2x less DRAM capacity than native Spark and Giraph, respectively. Finally, it outperforms Panthera, a garbage collector for hybrid memories, by up to 69%.

cs.PL↗

arXiv2021

NUMAscope: Capturing and Visualizing Hardware Metrics on Large ccNUMA Systems

Cache-coherent non-uniform memory access (ccNUMA) systems enable parallel applications to scale-up to thousands of cores and many terabytes of main memory. However, since remote accesses come at an increased cost, extra measures are necessitated to scale the applications to high core-counts and process far greater amounts of data than a typical server can hold. In a similar manner to how applications are optimized to improve cache utilization, applications also need to be optimized to improve data-locality on ccNUMA systems to use larger topologies effectively. The first step to optimizing an application is to understand what slows it down. Consequently, profiling tools, or manual instrumentation, are necessary to achieve this. When optimizing applications on large ccNUMA systems, however, there are limited mechanisms to capture and present actionable telemetry. This is partially driven by the proprietary nature of such interconnects, but also by the lack of development of a common and accessible (read open-source) framework that developers or vendors can leverage. In this paper, we present an open-source, extensible framework that captures high-rate on-chip events with low overhead (<10% single-core utilization). The presented framework can operate in live or record mode, allowing both real-time monitoring or capture for later post-workload or offline analysis. High-resolution visualization is available either through a standards-based (web) interactive graphical interface or through a convenient textual interface for quick-look analysis.

cs.DC↗