Peter, There are a few optimizations that h5repack does. For example, when rewriting chunked data h5repack uses H5Ocopy if applied filters and chunk sizes stay the same. It also uses hyperslab selections to coincide with the chunk boundaries and avoids datatype conversion if possible.
The comparison with h5repack may not be fair. For example, when an application reads compressed data time will be spend in decoding, while h5repack avoids the decoding step completely. Have you profiled your application to see where the time is spent? Elena ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Elena Pourmal The HDF Group http://hdfgroup.org 1800 So. Oak St., Suite 203, Champaign IL 61820 217.531.6112 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ On Sep 6, 2013, at 2:28 PM, Steinberg, Peter wrote: > My applications save a good-sized hdf5 dataset. > > It takes a fairly long time to read back in (around 4 minutes). > > If I do a simple repack on the file (h5repack infile outfile) reading it back > in only takes around 1 minute. > > What’s h5repack doing that speeds up the reads so much, and how do I > implement that in my application? > > (I was using h5repack to test different chunking sizes, and everything I did > in h5repack gave a similar time, including repacking to the same chunking > scheme as the original dataset). > > Thanks, > Peter Steinberg > _______________________________________________ > Hdf-forum is for HDF software users discussion. > [email protected] > http://mail.lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
_______________________________________________ Hdf-forum is for HDF software users discussion. [email protected] http://mail.lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org
