Improve performance of SaveNexus for eventWS

[Nick Draper]

From Garrett:

If I do the following two things,

1) load an event nexus into a workspace
2) right click and press save Nexus

It takes all of 7.57 seconds to read it in then it takes 725 seconds to save it.
I think there is some optimization needed in the save command.

what this means is that if I have say 10 workspaces and save a .mantid file,  it takes forever.

Also the progress bar does not at advance.

[Janik Zikovsky]

This refs #1525: SaveNexus is not finished for event workspaces.

[Janik Zikovsky]

(In [9342]) Refs #1525, #2268, #2269, #2355: SaveNexusProcessed and LoadNexusProcessed for event workspaces.

[Janik Zikovsky]

(In [9369]) Refs #2355: fix occasional segfault in tests.

[Janik Zikovsky]

(In [9377]) Refs #2355

[Janik Zikovsky]

SaveNexus is significantly faster and there is progress reporting. A file that takes 18 seconds to load takes 88 seconds to save - that it is still fairly slow but that is limited by Nexus writing - see ticket #2342.

[Michael Whitty]

File saved can not be loaded (in [9515])

Steps to reproduce:

• Load CNCS_7860_event.nxs using LoadEventNexus
• Right click on workspace, select 'Save Nexus'
• Try to run either LoadNexus or LoadNexusProcessed, you receive error message "bad allocation".

[Janik Zikovsky]

Are you using windows. I tried to reproduce the error on Linux but could not. See also ticket #2419.

[Michael Whitty]

Yes, I am using windows xp 32bit.

[Janik Zikovsky]

(In [10638]) Refs #2355. Some attempts were made at parallelizing writing NXS but HDF does not seem to support that. Compression is the bottleneck.

[Janik Zikovsky]

Speed comparison depending on the type of compression in NEXUS format. The file is TOPAZ_2170_events, loaded then saved as SaveNexusProcessed.

• Uncompressed: 38 seconds to write 2.2 GB.
• LZW compression (default): 308 seconds to write 1.3 GB.
• SZIP compression: 56 seconds to write 1.7 GB. SZIP requires HDF with SZIP enabled, available from the HDF site but not from repository (license issues).

[Janik Zikovsky]

(In [10639]) Refs #2355: Compression disabled for eventowrkspaces, for speed.

[Janik Zikovsky]

See #2342 for changes related to SZIP (if any).

[Stuart Campbell]

This ticket has been transferred to github issue ​3202