On Fri, Apr 1, 2011 at 9:00 AM, maha <m...@umail.ucsb.edu> wrote: > Hello Everyone, > > As far as I know, when my java program opens a sequence file for a map > calculations, from hdfs. Using SequenceFile.Reader(key,value) will actually > read the file in dfs.block.size then grabes record-by-record from memory. > > Is that right?
The dfs.block.size part is partially right when applied in MapReduce (actually, it would look for sync points for read start and read end). And no, the reader does not load the entire data in the memory in one-go. It buffers and reads off the stream just like any other reader. Could we have some more information on what your java program does, and what exactly you are measuring? :) -- Harsh J http://harshj.com
