Unable to read column family using pycassa

Question

I've just started using pycassa, so if this is a stupid question, I apologize upfront.

I have a column family with the following schema:

create column family MyColumnFamilyTest
  with column_type = 'Standard'
  and comparator = 'CompositeType(org.apache.cassandra.db.marshal.UTF8Type,org.apache.cassandra.db.marshal.UTF8Type,org.apache.cassandra.db.marshal.UTF8Type,org.apache.cassandra.db.marshal.TimeUUIDType)'
  and default_validation_class = 'BytesType'
  and key_validation_class = 'UTF8Type'
  and read_repair_chance = 0.1
  and dclocal_read_repair_chance = 0.0
  and populate_io_cache_on_flush = false
  and gc_grace = 864000
  and min_compaction_threshold = 4
  and max_compaction_threshold = 32
  and replicate_on_write = true
  and compaction_strategy = 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'
  and caching = 'KEYS_ONLY'
  and compression_options = {'sstable_compression' : 'org.apache.cassandra.io.compress.SnappyCompressor'};

When I try to do a get() with a valid key (works fine in cassandra-cli) I get:

Traceback (most recent call last):
  File "<pyshell#19>", line 1, in <module>
    cf.get('mykey',column_count=3)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 664, in get
    return self._cosc_to_dict(list_col_or_super, include_timestamp, include_ttl)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 368, in _cosc_to_dict
    ret[self._unpack_name(col.name)] = self._col_to_dict(col, include_timestamp, include_ttl)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 444, in _unpack_name
    return self._name_unpacker(b)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 140, in unpack_composite
    components.append(unpacker(bytestr[2:2 + length]))
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 374, in <lambda>
    return lambda v: uuid.UUID(bytes=v)
  File "/usr/lib/python2.7/uuid.py", line 144, in __init__
    raise ValueError('bytes is not a 16-char string')
ValueError: bytes is not a 16-char string

Here's some more information I've discovered:

When using cassandra-cli I can see the data as:

% cassandra-cli -h 10.249.238.131

Connected to: "LocalDB" on 10.249.238.131/9160
Welcome to Cassandra CLI version 1.2.10-SNAPSHOT

Type 'help;' or '?' for help.
Type 'quit;' or 'exit;' to quit.

[default@unknown] use Keyspace;
[default@Keyspace] list ColumnFamily;
Using default limit of 100
Using default cell limit of 100
-------------------
RowKey: urn:keyspace:ColumnFamily:a36e8ab1-7032-4e4c-a53d-e3317f63a640:
=> (name=autoZoning:::, value=01, timestamp=1391298393966000)
=> (name=creationTime:::, value=00000143efd8b76e, timestamp=1391298393966000)
=> (name=inactive:::14fe78e0-8b9b-11e3-b171-005056b700bb, value=00, timestamp=1391298393966000)
=> (name=label:::14fe78e0-8b9b-11e3-b171-005056b700bb, value=726a6d2d766e782d76613031, timestamp=1391298393966000)

1 Row Returned.
Elapsed time: 16 msec(s).

Since it was unclear what was causing the exception, I decided to add a print prior to the 'return self._name_unpacker(b)' line in columnfamily.py and I see:

>>> cf.get(dict(cf.get_range(column_count=0,filter_empty=False)).keys()[0])
Attempting to unpack: <00>\rautoZoning<00><00><00><00><00><00><00><00><00><00>

Traceback (most recent call last):
  File "<pyshell#172>", line 1, in <module>
    cf.get(dict(cf.get_range(column_count=0,filter_empty=False)).keys()[0])
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 665, in get
    return self._cosc_to_dict(list_col_or_super, include_timestamp, include_ttl)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 368, in _cosc_to_dict
    ret[self._unpack_name(col.name)] = self._col_to_dict(col, include_timestamp, include_ttl)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 445, in _unpack_name
    return self._name_unpacker(b)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 140, in unpack_composite
    components.append(unpacker(bytestr[2:2 + length]))
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 374, in <lambda>
    return lambda v: uuid.UUID(bytes=v)
  File "/usr/lib/python2.7/uuid.py", line 144, in __init__
    raise ValueError('bytes is not a 16-char string')
ValueError: bytes is not a 16-char string

I have no idea where the extra characters are coming from around the column name. But that got me curious so I added another print in _cosc_to_dict in columnfamily.py and I see:

    >>> cf.get(dict(cf.get_range(column_count=0,filter_empty=False)).keys()[0])
    list_col_or_super is: []
    list_col_or_super is: [ColumnOrSuperColumn(column=Column(timestamp=1391298393966000, 
name='\x00\rautoZoning\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', value='\x01', ttl=None), 
counter_super_column=None, super_column=None, counter_column=None), 
ColumnOrSuperColumn(column=Column(timestamp=1391298393966000, 
name='\x00\x0ccreationTime\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 
value='\x00\x00\x01C\xef\xd8\xb7n', ttl=None), counter_super_column=None, super_column=None, 
counter_column=None), ColumnOrSuperColumn(column=Column(timestamp=1391298393966000, 
name='\x00\x08inactive\x00\x00\x00\x00\x00\x00\x00\x00\x10\x14\xfex\xe0\x8b\x9b\x11\xe3\xb1q\x00PV\xb7\x00\xbb\x00', value='\x00', ttl=None), counter_super_column=None, super_column=None, 
counter_column=None), ColumnOrSuperColumn(column=Column(timestamp=1391298393966000, 
name='\x00\x05label\x00\x00\x00\x00\x00\x00\x00\x00\x10\x14\xfex\xe0\x8b\x9b\x11\xe3\xb1q\x00PV\xb7\x00\xbb\x00', value='thisIsATest', ttl=None), counter_super_column=None, super_column=None, counter_column=None)]
    autoZoning unpack: 
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/usr/local/lib64/python2.6/site-packages/pycassa-1.11.0-py2.6.egg/pycassa/columnfamily.py", line 666, in get
        return self._cosc_to_dict(list_col_or_super, include_timestamp, include_ttl)
      File "/usr/local/lib64/python2.6/site-packages/pycassa-1.11.0-py2.6.egg/pycassa/columnfamily.py", line 369, in _cosc_to_dict
        ret[self._unpack_name(col.name)] = self._col_to_dict(col, include_timestamp, include_ttl)
      File "/usr/local/lib64/python2.6/site-packages/pycassa-1.11.0-py2.6.egg/pycassa/columnfamily.py", line 446, in _unpack_name
        return self._name_unpacker(b)
      File "/usr/local/lib64/python2.6/site-packages/pycassa-1.11.0-py2.6.egg/pycassa/marshal.py", line 140, in unpack_composite
        components.append(unpacker(bytestr[2:2 + length]))
      File "/usr/local/lib64/python2.6/site-packages/pycassa-1.11.0-py2.6.egg/pycassa/marshal.py", line 374, in <lambda>
        return lambda v: uuid.UUID(bytes=v)
      File "/usr/lib64/python2.6/uuid.py", line 144, in __init__
        raise ValueError('bytes is not a 16-char string')
    ValueError: bytes is not a 16-char string

Am I correct in assuming that the extra characters around the column names are what is responsible for the 'ValueError: bytes is not a 16-char string' exception?

Also if I try to use the column name and select it I get:

>>> cf.get(u'urn:keyspace:ColumnFamily:a36e8ab1-7032-4e4c-a53d-e3317f63a640:',columns=['autoZoning:::'])

Traceback (most recent call last):
  File "<pyshell#184>", line 1, in <module>
    cf.get(u'urn:keyspace:ColumnFamily:a36e8ab1-7032-4e4c-a53d-e3317f63a640:',columns=['autoZoning:::'])
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 651, in get
    cp = self._column_path(super_column, column)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 383, in _column_path
    self._pack_name(column, False))
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/columnfamily.py", line 426, in _pack_name
    return self._name_packer(value, slice_start)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 115, in pack_composite
    packed = packer(item)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/marshal.py", line 298, in pack_uuid
    randomize=True)
  File "/usr/local/lib/python2.7/dist-packages/pycassa-1.11.0-py2.7.egg/pycassa/util.py", line 75, in convert_time_to_uuid
    'neither a UUID, a datetime, or a number')
ValueError: Argument for a v1 UUID column name or value was neither a UUID, a datetime, or a number

Any further thoughts?

Thanks,

Rob

Answer 1

Turns out that the problem wasn't with the key, it was being caused, in part, by a bug in pycassa that wasn't handling an empty (null) string in the column UUID. A short-term fix is in the answer in google groups:

https://groups.google.com/d/msg/pycassa-discuss/Vf_bSgDIi9M/KTA1kbE9IXAJ

The other part of the answer was to get at the columns by using tuples (with the UUID as a UUID and not a str) instead of a string with ':' separators because that's, as I found out, a cassandra-cli thing.