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Storing and processing massive small files is one of the major challenges for the Hadoop Distributed File System (HDFS). In order to provide fast data access, the NameNode (NN) in HDFS maintains the metadata of all files in its main-memory. Hadoop performs well with a small number of large files that require relatively little metadata in the NN s memory. But for a large number of small files, Hadoop has problems such as NN memory overload caused by the huge metadata size of these small files. We present a new type of archive file, Hadoop Perfect File (HPF), to solve HDFS s small files problem by merging small files into a large file on HDFS. Existing archive files offer limited functionality and have poor performance when accessing a file in the merged file due to the fact that during metadata lookup it is necessary to read and process the entire index file(s). In contrast, HPF file can directly access the metadata of a particular file from its index file without having to process it entirely. The HPF index system uses two hash functions: file s metadata are distributed through index files by using a dynamic hash function and, for each index file, we build an order preserving perfect hash function that preserves the position of each file s metadata in the index file. The HPF design will only read the part of the index file that contains the metadata of the searched file during its access. HPF file also supports the file appending functionality after its creation. Our experiments show that HPF can be more than 40% faster file s access from the original HDFS. If we don t consider the caching effect, HPF s file access is around 179% faster than MapFile and 11294% faster than HAR file. If we consider caching effect, HPF is around 35% faster than MapFile and 105% faster than HAR file.

Two kinds of copper oxide with different particle sizes and 1.5 μm tungsten trioxide powder were employed to prepare the high-purity CuWO4 powder. By two stage hydrogen-reduction of the CuWO4 at 360 and 750 °C respectively and continuously, nano-composite powder of tungsten coated copper was synthesized. Micro-morphology, crystallization-components and grain-size of the products were investigated by scanning electron microscope (SEM), X-ray diffract meter (XRD) and transmission electric microscope (TEM) and laser particle size analyzer (LPSA) was also applied to measure the particle-size of CuWO4. The W film thickness of nano-composite powder synthesized by smaller-sized CuWO4 is thinner than that made from bigger-sized CuWO4. The average particle size of nano-composite powder of tungsten coated copper is about 50 nm under the two-stage hydrogen reduction.

In this paper, we propose a method of feature matching based asymmetric three-dimensional (3D) image coding with hierarchical reconstruction quality. At the encoder, for the main view the standard intra coding can be applied to obtain high reconstruction quality while for its neighboring views extracted feature descriptors can be utilized to calculate transformation matrix between views. The parameters of transformation matrix can be transmitted by very low bit rate and achieve the preliminary reconstruction. Furthermore, the residues can be exploited to improve the performance. The experimental results have shown that the proposed scheme can reach a very high compression ratio.