无法使用pycassa读取列族

Question

我刚刚开始使用pycassa，所以如果这是一个愚蠢的问题，我很抱歉。

我有一个具有以下架构的列族：

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'};

当我尝试用一个有效的键执行get()时(在cassandra-cli中工作得很好)，我得到：

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

下面是我发现的更多信息：

当使用cassandra-cli时，我可以看到如下数据：

% 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).

由于不清楚是什么导致了异常，我决定在columnfamily.py中的'return self._name_unpacker(b)‘行之前添加一个打印，我看到了：

>>> 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

我不知道列名周围的额外字符来自哪里。但这让我很好奇，所以我在columnfamily.py的_cosc_to_dict中添加了另一个打印，我看到了：

    >>> 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

我假设列名周围的额外字符是导致'ValueError: bytes is not a 16-char string‘异常的原因，对吗？

另外，如果我尝试使用列名并选择它，我会得到：

>>> 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

还有进一步的想法吗？

谢谢,

抢夺

Answer 1

原来问题不是键的问题，而是由pycassa中的一个bug引起的，该bug没有处理列UUID中的空(null)字符串。谷歌群组的答案中有一个短期的解决办法：

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

答案的另一部分是通过使用元组(将UUID作为UUID而不是str)来获取列，而不是使用带有':‘分隔符的字符串，因为我发现这是cassandra-cli的事情。