Error with reading/writing a lot of large hdf5 files
I am using pandas to read/write a lot of relatively large hdf5 files (hundreds MB each), hundreds of them, using HDFStore. My app acts as a service and I am facing seg faults after it runs for some time. It seems that it seg fault after some random HDF error occurs. I am able to cause some HDF errors by repeatedly read/write a relatively large HDF files:

``` python
import pandas as pd
import numpy as np

db = pd.HDFStore('test.h5','w')
for i in range(1000): db[str(i)] = pd.DataFrame(np.random.rand(2000,3),columns=['a','b','c'])
db.close()
for i in range(100):
        f="test.h5"
        print i
        db=pd.HDFStore(f,mode='r')
        db2=pd.HDFStore(f+'.new',mode='w')
        for k in db.keys(): db2[k] = db[k]
        db2.close()
        db.close()
```

After some time the following error occurs:

TypeError                                 Traceback (most recent call last)
<ipython-input-2-c47d3a0893ae> in <module>()
      4         db=pd.HDFStore(f,mode='r')
      5         db2=pd.HDFStore(f+'.new',mode='w')
----> 6         for k in db.keys(): db2[k] = db[k]
      7         db2.close()
      8         db.close()

/usr/lib/python2.7/site-packages/pandas/io/pytables.pyc in **getitem**(self, key)
    414 
    415     def **getitem**(self, key):
--> 416         return self.get(key)
    417 
    418     def **setitem**(self, key, value):

/usr/lib/python2.7/site-packages/pandas/io/pytables.pyc in get(self, key)
    618         if group is None:
    619             raise KeyError('No object named %s in the file' % key)
--> 620         return self._read_group(group)
    621 
    622     def select(self, key, where=None, start=None, stop=None, columns=None,

/usr/lib/python2.7/site-packages/pandas/io/pytables.pyc in _read_group(self, group, **kwargs)
   1276         s = self._create_storer(group)
   1277         s.infer_axes()
-> 1278         return s.read(**kwargs)
   1279 
   1280 

/usr/lib/python2.7/site-packages/pandas/io/pytables.pyc in read(self, **kwargs)
   2656         axes = []
   2657         for i in range(self.ndim):
-> 2658             ax = self.read_index('axis%d' % i)
   2659             axes.append(ax)
   2660 

/usr/lib/python2.7/site-packages/pandas/io/pytables.pyc in read_index(self, key)
   2258             return index
   2259         else:  # pragma: no cover
-> 2260             raise TypeError('unrecognized index variety: %s' % variety)
   2261 
   2262     def write_index(self, key, index):

TypeError: unrecognized index variety: None

It is not the necessary the same error happening in my real system but it seems the error occurred is not always the same.

In [7]: pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.8.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-30-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.14.1
nose: None
Cython: 0.20.2
numpy: 1.8.2
scipy: None
statsmodels: None
IPython: 2.2.0
sphinx: None
patsy: None
scikits.timeseries: None
dateutil: 2.2
pytz: 2014.4
bottleneck: None
tables: 3.1.1
numexpr: 2.4
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
rpy2: 2.4.3
sqlalchemy: 0.9.7
pymysql: None
psycopg2: None
