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46results about How to "Eliminate calculations" patented technology

Data storage control method and apparatus for external storage device using a plurality of flash memories

The present invention is to realize a data storage control method and apparatus for an external storage device using flash memories. The method and apparatus can eliminate the data erasure waiting time, eliminating the calculation of the erasure numbers of flash memories, elongating the life-time of the flash memories. Data is stored sequentially from a first flash memory for rewrite data to a third flash memory for rewrite data. When there is no vacant area in the third flash memory for rewrite data, a CPU instructs a first flash memory for garbage collection among the first and second flash memories for garbage collection to perform the garbage collection of the first flash memory for rewrite data. When a host computer issues a write access request, the write process is performed in the first flash memory for garbage collection with the first priority. When the garbage collection of the first flash memory for rewrite data has been completed, the garbage collection of the second flash memory for rewrite data is performed by the second flash memory for garbage collection. At the time of performing the garbage collection of the second flash memory for rewrite data, the data of the first flash memory for rewrite data is simultaneously erased. The first flash memory for garbage collection is changed into a flash memory for rewrite data by the CPU. Upon completion of the garbage collection of the second flash memory for rewrite data, the data thereof is simultaneously erased and the second flash memory for garbage collection is changed into a flash memory for rewrite data. Then, the garbage collection of the third flash memory for rewrite data is performed in the similar manner.
Owner:HITACHI LTD

Query optimization method based on join index in data warehouse

The invention relates to a query optimization method based on a join index in a data warehouse. The method comprises the following steps: creating a fact table foreign key join index based on a dimension table surrogate key; creating a join index update strategy; when a predicate condition exists on a dimension table, making a predicate judgment after direct access to dimension table record through the join index, and performing calculation through a dynamic bitmap join index by reference to a bitmap join index to generate a join bitmap index; when the selection rate on the dimension table is very low, further compressing a dimension table bitmap in order to raise the cache level of dimension table bitmap calculation; and calculating simple memory address access by only using an array-bitmap data structure with a reference bitmap join index calculation method based on co-processor memory calculation. Through adoption of the query optimization method, the calculation performance of the bitmap index can be effectively increased. Moreover, the query optimization method can be combined with high-performance co-processors such as GPU and Intel Xeon Phi TM to accelerate the index calculation performance, and can be widely applied to the field of data warehouses.
Owner:RENMIN UNIVERSITY OF CHINA
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