Dear Mian Lu, Thanks for your interest in FastBit work. I have just checked the source code that implements the option to decompess bitmaps, it is still there.
It sounds like you have the indexes already in the data directory. To force the indexes to be rebuilt, you might want to add -z following -b option. You shouldn't need that, but it explicitly forces the existing indexes to be removed. Another thing to keep in mind is that each uncompressed index must fit in the memory. If you have high-cardinality data, this can be a challenge. FastBit builds the compressed indexes first and then decompress the bitmaps on request. If it fails to decompress them, it will keep on using the compressed version -- there should be some warning message about this sort of thing if the verboseness level is a positive number. If you plan to measure the query processing time using the uncompressed index, you might find that it is not what you expect. In the current version of the software, the raw data is assumed to be present. Therefore, to evaluate any query, there are at least two options, using the index and using the raw data (which is a vertical projection only, not the whole relation). The decision on which one to use is based on which option will access less bytes. If the index is uncompressed, then it is much more likely that using the index will read more bytes than using the vertical projection. The result is that you will not see how the uncompressed index behaves. To modify this behavior, you need to edit the function ibis::column::evaluateRange. if you only want to test the performance of some simple range conditions, the version of this function you want starts at line 4911 in src/column.cpp. Hope this helps. John On 10/11/2009 8:02 AM, Mian Lu wrote: > Dear Dr. Wu: > > I am a third year Ph.D. student from Hong Kong University of Science and > Technology. Currently, I am very interested in your FastBit project. > However, for research purpose, I want to get the equality encoding bitmap > index without any compressions. I have tried the command line in your > document, like this > > examples/ibis -v -d tmp -b "<binning none/><encoding > equality/><compressing uncompressAll/>" > > However, it looks like no effect. The index should be still built with > compressions (the size is not changed). I would like to ask whether such > options have been removed, please? I really appreciate if you can still > provide the bitmap without any compressions. Thanks very much. > > Regards, > Mian Lu > _______________________________________________ FastBit-users mailing list [email protected] https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users
