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I already announced Pcap inputformat module for large pcap trace file distributed into more than one block. The paper,"A Hadoop-based Packet Trace Processing Tool" also pronounced in TMA 2011. To handle large pcap trace file, I devised heuristic algorithm and implemented packet trace analysis tool, which benchmarked CAIDA's CoralReef tool and source code was also released publicly. But, my concern is that my pcap input format module name is PcapInputFormat which is same with yours. In my opinion, the functionality is different. Yours just make the pcap file do not splitable and process whole file with one thread. That's the reason why performance is not good.