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Dr. Hadoop: an infinite scalable metadata management for Hadoop—How the baby elephant becomes immortal
Dipayan DEV,Ripon PATGIRI
Front. Inform. Technol. Electron. Eng.    2016, 17 (1): 15-31.   DOI: 10.1631/FITEE.1500015
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In this Exa byte scale era, data increases at an exponential rate. This is in turn generating a massive amount of metadata in the file system. Hadoop is the most widely used framework to deal with big data. Due to this growth of huge amount of metadata, however, the efficiency of Hadoop is questioned numerous times by many researchers. Therefore, it is essential to create an efficient and scalable metadata management for Hadoop. Hash-based mapping and subtree partitioning are suitable in distributed metadata management schemes. Subtree partitioning does not uniformly distribute workload among the metadata servers, and metadata needs to be migrated to keep the load roughly balanced. Hash-based mapping suffers from a constraint on the locality of metadata, though it uniformly distributes the load among NameNodes, which are the metadata servers of Hadoop. In this paper, we present a circular metadata management mechanism named dynamic circular metadata splitting (DCMS). DCMS preserves metadata locality using consistent hashing and locality-preserving hashing, keeps replicated metadata for excellent reliability, and dynamically distributes metadata among the NameNodes to keep load balancing. NameNode is a centralized heart of the Hadoop. Keeping the directory tree of all files, failure of which causes the single point of failure (SPOF). DCMS removes Hadoop’s SPOF and provides an efficient and scalable metadata management. The new framework is named ‘Dr. Hadoop’ after the name of the authors.




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Algorithm 1 Write operation of Dr. Hadoop in DCMS
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The dynamic circular metadata splitting of the Dr. Hadoop framework is a circular arrangement of NameNodes. The internal architecture of a NameNode (metadata server) is shown in Fig. 1 and it is a part of the circular arrangement of DCMS. The hashtable storage manager keeps a hashtable to store the key-value of metadata. It also administers an SHA1 (U.S. Department of Commerce/NIST, 1995) based storage system under two components, i.e., a replication engine and failover management. The replication engine features the redundancy mechanisms and determines the throughput of read or write metadata in the DCMS.
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