Appallingly slow loading of history from a nexus processed file

[mantid-builder]

Original Reporter: Russell Taylor

The attached file takes about 20 seconds to load, almost all of which is related to the loading of the algorithm history. I've worked out exactly where the problem is, but I don't know enough about the nexus library, or more particularly our wrappers around it, to work out how to fix it.

The problem lines are lines 415 & 416 of LoadNexusProcessed.cpp, which, within the enclosing loop, each account for ~10 seconds of the algorithm duration:

  NXNote entry = history.openNXNote(itr->nxname);
  const std::vector`<std::string>` & info = entry.data();

The underlying slow method behind the first line is NXClass::openNXClass, that behind the second line is NXClass::openNXChar. I think they both wind up calling the NXClass::open method.

[mantid-builder]

This issue was originally trac ticket 1074

[mantid-builder]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/1074/van_s2_new_corr-0.nxs
(uploaded by Russell Taylor on 2009-12-16T11:02:55)

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