We present SGuard, a new fault-tolerance technique for distributed stream processing engines (SPEs) running in clusters of commodity servers. SGuard is less disruptive to normal stream processing and leaves more resources available for normal stream processing than previous proposals. Like several previous schemes, SGuard is based on rollback recovery [18]: it checkpoints the state of stream processing nodes periodically and restarts failed nodes from their most recent checkpoints. In contrast to previous proposals, however, SGuard performs checkpoints asynchronously: i.e., operators continue processing streams during the checkpoint thus reducing the potential disruption due to the checkpointing activity. Additionally, SGuard saves the checkpointed state into a new type of distributed and replicated file system (DFS) such as GFS [22] or HDFS [9], leaving more memory resources available for normal stream processing. To manage resource contention due to simultaneous checkpoints by different SPE nodes, SGuard adds a scheduler to the DFS. This scheduler coordinates large batches of write requests in a manner that reduces indvidual checkpoint times while maintaining good overall resource utilization. We demonstrate the effectiveness of the approach through measurements of a prototype implementation in the Borealis [2] open-source SPE using HDFS [9] as the DFS.
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