Unable to load in derivable arrays in server mode

[mtremmel]

When attempting to run a calculation that uses load-mode=server, the process crashes on a step where it is attempting to load in a derivable array (in this case, "ne" for gas particles). This does not occur when running with load-mode=partial. The error comes as a KeyError for gas family.

a5310> applied to <Halo u'h1.cosmo50/h1.cosmo50PLK.1536gst1bwK1BH.003935/halo_1' | NDM=356536379 Nstar=95801512 Ngas=83888973>
Traceback (most recent call last):
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/tangos-1.0.dev0-py2.7.egg/tangos/tools/property_writer.py", line 370, in _get_prope
rty_value
    result = property_calculator.calculate(snapshot_data, db_data)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/tangos-1.0.dev0-py2.7.egg/michaels_properties/profiles.py", line 94, in calculate
    rho_e = ps['rho_e']
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/analysis/profile.py", line 434, in __ge
titem__
    return self._get_profile(name)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/analysis/profile.py", line 346, in _get
_profile
    self._profiles[name] = Profile._profile_registry[x[0]](self, *args)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/tangos-1.0.dev0-py2.7.egg/michaels_properties/profiles.py", line 50, in rho_e
    n_e[i] = np.sum(subs.g['ne'][use] * subs.g['mass'][use].in_units('m_p'))/self._binsize.in_units('cm**'+str(int(self.ndim)))[i]
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/snapshot/__init__.py", line 263, in __g
etitem__
    return self._get_array_with_lazy_actions(i)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/snapshot/__init__.py", line 358, in _ge
t_array_with_lazy_actions
    return self._get_array(name)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/snapshot/__init__.py", line 1909, in _g
et_array
    return self.base._get_family_array(name, self._unifamily, index, always_writable)
  File "/u/mtremmel/anaconda/lib/python2.7/site-packages/pynbody-0.41-py2.7-linux-x86_64.egg/pynbody/snapshot/__init__.py", line 1852, in _g
et_family_array
    sl = self._family_indices[fam]
KeyError: <Family gas>```

[apontzen]

Could you make your michaels_properties module available somewhere so I can reproduce the exact issue?

[mtremmel]

I have a forked version... I think you can access it? It was forked from the original halo_database repository... how it is a part of pynbody. Not sure if that matters right now.

github.com/mtremmel/halo_database

[apontzen]

OK I think quite a complex range of things have happened here.

First, there is something slightly strange about how _family_indices is getting set which I don't quite understand. However this seems trivially fixable by changing line 1852 of pynbody's pynbody/snapshot/__init__.py to sl = self._family_indices.get(fam,None) (was originally sl = self._family_indices[fam])

Then there is something more annoying but more understandable. Basically the ne property is specific to TipsySnap (see line 980 of pynbody/snapshot/tipsy.py forwards). But the snapshot is now of type RemoteSnap, not TipsySnap. This requires a more permanent fix but for now could you try changing all the TipsySnap.derived_quantity to SimSnap.derived_quantity in your tipsy.py.

With these two modifications does your code operate correctly? If so we have identified the problem and can move onto figuring out more permanent fixes.

[mtremmel]

Tried load-mode=server with those changes and it works! So the problem has been found.

[apontzen]

Permanent fix for this proposed in PR #5

@mtremmel please see if this works for you! Ignore the fact that the Travis tests are failing - this seems to be some py3.5-specific issue with a library somewhere; I'll track this down in the meantime.

[apontzen]

I've merged but will wait to hear whether it fixes the original problem before closing the issue