On 25/08/11 07:54, Anders Logg wrote: > On Thu, Aug 25, 2011 at 07:45:49AM -0400, Garth N. Wells wrote: > >>> Sure, but I would claim SAX scales better. >> >> In terms of memory, yes. >> >> It is not sufficiently scalable to be a total solution. Plus it's too slow. > > Agree. > >>> Wouldn't it be better to >>> just use one of DOM or SAX? >> >> Maybe. A SAX implementation is considerably more complex. The new >> implementation reserves this complexity for a possibly critical case and >> localises the complexity of the code. The old code was very complex and >> less localised. >> >> The locality means that it's no big deal to have a simple DOM >> implementation for the majority of cases next to a more complex SAX >> implementations for special cases. There is no point in the size and >> complexity of a SAX parser for simple cases, e.g. reading parameter files. > > Agree, but see below. > >>> Either we use SAX all the way if it gives >>> better performance than DOM, >> >> It doesn't give better performance. We discussed this before. Without >> checking the archive, I recall that the DOM implementation was about 50 >> times faster for large data sets than the old SAX implementation. >> >>> or we use DOM all the way as a solution >>> for medium sized problems and complement with HDF5 for large scale >>> problems. Having DOM + SAX + HDF5 seems messy. >>> >> >> This may happen, but the fact is that we don't have HDF5 in place yet. >> >>>>>>> What is the difference between XMLLocalMeshData and >>>>>>> XMLLocalMeshDataDistributed etc. >>>>>>> >>>>>> >>>>>> Initially I planned to use DOM for all, but as outlined above decided >>>>>> after some testing to retain SAX for meshes (but update to SAX2, since >>>>>> the libxml2 SAX parser is deprecated and has memory leaks). Hence, >>>>>> XMLLocalMeshData uses DOM and XMLLocalMeshDataDistributed uses SAX. So >>>>>> far I've kept the DOM version since it's easy to code and could be >>>>>> useful when reading non-distributed meshes on each process (which may >>>>>> differ on different processes). >>>>> >>>>> I don't understand the difference between XMLLocalMeshData and >>>>> XMLLocalMeshDataDistributed. Is XMLLocalMeshDataDistributed doing now >>>>> what XMLLocalMeshData did before? >>>>> >>>> >>>> Yes, but updated to SAX2 (which was very painful). >>>> >>>> The 'new' XMLLocalMeshData is a DOM version. It could be removed. >>> >>> Or kept if we will add HDF5 anyway as a more scalable solution. >>> >> >> Again, it may be desirable to keep a SAX parser for reading meshes in >> parallel since a mesh is the most likely large data structure to be >> created externally, and the most complex. HDF5 would require a user to >> supply a binary mesh file rather than an XML file. Most other large data >> sets are created internally, and the read and written. In this case, >> HDF5 will be fine. > > How about using DOM everywherme and reserve the use of SAX for an > XML->HDF5 converter? >
That could be OK, but if we have the to implement a SAX parser it's probably easiest to have it in DOLFIN anyway. I don't see the advantage over having the SAX parser with the io code. Garth > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
