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From Jack Culpepper <jackculpep...@gmail.com>
Subject Re: get_key_range() vs. get_range_slice() -- scan/counting errors
Date Mon, 08 Feb 2010 22:33:19 GMT
Done. CASSANDRA-781

On Mon, Feb 8, 2010 at 2:06 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
> Can you create a ticket for this, please?  Thanks!
>
> On Sat, Feb 6, 2010 at 7:05 PM, Jack Culpepper <jackculpepper@gmail.com> wrote:
>> I did a bit more testing, and it does seem to be related to having two
>> nodes. When I turn one node off and repeat the range scan, I get the
>> same result, but if I start with only one node and do all the inserts
>> and then a range scan, I get the correct count using
>> get_range_slice().
>>
>> However, with two nodes there is a very easy way to replicate the
>> problem. Just clear out your Test Keyspace and insert 1000 keys. For
>> example, here I use pycassa to do that.
>>
>> if 1:
>>    import pycassa
>>    import uuid
>>
>>    client = pycassa.connect(["10.212.87.165:9160"])
>>    cf_test = pycassa.ColumnFamily(client, "Test Keyspace", "Test
>> Super", super=True)
>>
>>    for i in xrange(1000):
>>        key = uuid.uuid4().hex
>>        cf_test.insert(key, { 'params' : { 'is' : 'cool' }})
>>        print key
>>
>> Hear me out before you argue that pycassa is the problem. I haven't
>> actually done this using the raw thrift interface, but only the
>> retrieval is problemic. You can run this code and pipe the output to a
>> file to record all the keys that were inserted. Now use the regular
>> thrift interface to try and get them back:
>>
>> if 1:
>>    from thrift import Thrift
>>    from thrift.transport import TTransport
>>    from thrift.transport import TSocket
>>    from thrift.protocol.TBinaryProtocol import TBinaryProtocolAccelerated
>>    from cassandra import Cassandra
>>    from cassandra.ttypes import *
>>
>>    socket = TSocket.TSocket("10.212.87.165", 9160)
>>    transport = TTransport.TBufferedTransport(socket)
>>    protocol = TBinaryProtocol.TBinaryProtocolAccelerated(transport)
>>    client = Cassandra.Client(protocol)
>>
>>    transport.open()
>>
>>
>>    column_parent = ColumnParent(column_family="Test Super")
>>    slice_range = SliceRange(start="key", finish="key")
>>    #slice_range = SliceRange(start="", finish="")
>>    predicate = SlicePredicate(slice_range=slice_range)
>>
>>    done = False
>>    seg = 1000
>>    start = ""
>>
>>    while not done:
>>        #result = client.get_key_range("Test Keyspace", "Test Super",
>> start, "", seg, ConsistencyLevel.ONE)
>>        result = client.get_range_slice("Test Keyspace",
>> column_parent, predicate, start, "", seg, ConsistencyLevel.ONE)
>>
>>        if len(result) < seg: done = True
>>        #else: start = result[seg-1]
>>        else: start = result[seg-1].key
>>
>>
>>        for r in result:
>>            #print r
>>            print r.key
>>
>> Using get_range_slice() I see only keys from
>> 562ab7792af249be8e73ba2ace5a5888 to 9fd73cf2ab264571a5654c315ab6e93d,
>> but with get_key_range() I see keys from
>> 01b12cdae9464d1ab4cf2f89808883d9 to ffda307823ee43eeac590a3201b81962.
>>
>> That is, get_key_range() retrieves *all* the keys, but
>> get_range_slice() does not. Thus, it seems unlikely that there is a
>> problem with pycassa or the way I did my insertions if get_key_range()
>> is able to work properly.
>>
>> I also just read through the "How to retrieve keys from Cassandra ?"
>> thread. I agree with Jean-Denis Greze that it would be nice to have a
>> method to retrieve all the keys at a particular node, instead of a
>> range of keys.
>>
>> Jack
>>
>> On Sat, Feb 6, 2010 at 2:01 PM, Jack Culpepper <jackculpepper@gmail.com> wrote:
>>> Well, from the output I included you can see that get_slice_range()
>>> does not return any keys above
>>> 9ffff14fd361b981faea6a04c5ef5699a96a8d6d, whereas get_key_range()
>>> finds keys all the way up to ffffffa1b5e3aeb9ca92d4d848280093bdf49892.
>>>
>>> My program stops if either function ever returns less keys than
>>> requested (1000 in this case).
>>>
>>> I have 2 nodes and a replication factor of 2, so both nodes should
>>> have all the data, right?
>>>
>>> If I turn off one node and try the same test, I get the same result --
>>> that is, get_key_range() finds many more key than get_slice_range(). I
>>> haven't tested the case where I delete all the data, launch only a
>>> single node and do all the inserts on a single node, and then compare
>>> both methods. If you would like me to do that I can.
>>>
>>> Jack
>>>
>>> On Sat, Feb 6, 2010 at 10:16 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
>>>> It would help if you could narrow it down to "here are the keys I
>>>> expect to see that I am not," especially if you can reproduce on a
>>>> single-node cluster.
>>>>
>>>> On Sat, Feb 6, 2010 at 2:04 AM, Jack Culpepper <jackculpepper@gmail.com>
wrote:
>>>>> Hi Jonathon,
>>>>>
>>>>> I am seeing a dramatic difference in the number of keys I can scan
>>>>> when I use these two methods.
>>>>>
>>>>> The former (deprecated) method seems to return the correct result.
>>>>> That is, it's on the right order of magnitude of around 500K, and if
I
>>>>> continue to insert keys via a separate process as I repeatedly count
>>>>> them, the count grows. The recommended alternative, get_range_slice(),
>>>>> returns far fewer keys and if I count repeatedly as I insert using a
>>>>> separate process, the count bounces around erratically.
>>>>>
>>>>> I am using the python thrift interface against a two node setup. I am
>>>>> running the current 0.5.0 release (just upgraded from rc1 since I saw
>>>>> some other thrift bug was fixed). Here is my program (there are three
>>>>> commented lines to switch from one method to the other):
>>>>>
>>>>> if sys.argv[1] == "count_things":
>>>>>
>>>>>    from thrift import Thrift
>>>>>    from thrift.transport import TTransport
>>>>>    from thrift.transport import TSocket
>>>>>    from thrift.protocol.TBinaryProtocol import TBinaryProtocolAccelerated
>>>>>    from cassandra import Cassandra
>>>>>
>>>>>    socket = TSocket.TSocket("10.212.230.176", 9160)
>>>>>    transport = TTransport.TBufferedTransport(socket)
>>>>>    protocol = TBinaryProtocol.TBinaryProtocolAccelerated(transport)
>>>>>    client = Cassandra.Client(protocol)
>>>>>
>>>>>    transport.open()
>>>>>
>>>>>    column_parent = ColumnParent(column_family="thing")
>>>>>    slice_range = SliceRange(start="key", finish="key")
>>>>>    predicate = SlicePredicate(slice_range=slice_range)
>>>>>
>>>>>    done = False
>>>>>    seg = 1000
>>>>>    start = ""
>>>>>
>>>>>    while not done:
>>>>>        #result = client.get_key_range("gg", "thing", start, "", seg,
>>>>> ConsistencyLevel.ONE)
>>>>>        result = client.get_range_slice("gg", column_parent,
>>>>> predicate, start, "", seg, ConsistencyLevel.ONE)
>>>>>
>>>>>        if len(result) < seg: done = True
>>>>>        #else: start = result[seg-1]
>>>>>        else: start = result[seg-1].key
>>>>>
>>>>>        record_count += len(result)
>>>>>
>>>>>        t = now()
>>>>>        dt = t - startTime
>>>>>        record_per_sec = record_count / dt
>>>>>        #print "\rstart %d now %d dt %d rec/s %.4f rec %d s %s f
>>>>> %s"%(startTime,t,dt,record_per_sec,record_count,result[0],result[-1]),
>>>>>        print "\rstart %d now %d dt %d rec/s %.4f rec %d s %s f
>>>>> %s"%(startTime,t,dt,record_per_sec,record_count,result[0].key,result[-1].key),
>>>>>    print
>>>>>
>>>>> An example of the output using get_range_slice(), without a concurrent
>>>>> insertion process -- it counts 133674 keys.
>>>>>
>>>>> start 1265440888 now 1265441098 dt 210 rec/s 636.1996 rec 133674 s
>>>>> 9f9dd2c0f043902f7f571942cfac3f6c28b82cec f
>>>>> 9ffff14fd361b981faea6a04c5ef5699a96a8d6d
>>>>>
>>>>> Using get_key_range() I get 459351 keys, and the throughput is less:
>>>>>
>>>>> start 1265442143 now 1265443092 dt 948 rec/s 484.2775 rec 459351 s
>>>>> ffce8099f808d10a09db471b04793315f555ccbd f
>>>>> ffffffa1b5e3aeb9ca92d4d848280093bdf49892
>>>>>
>>>>> get_range_slice() seems to skip keys in each of the segments.
>>>>>
>>>>> The "thing" column family is a super column. There are no errors
>>>>> reported to the log. The keys I am inserting are python generated
>>>>> UUIDs:
>>>>>
>>>>> import uuid
>>>>> key = uuid.uuid4().hex
>>>>>
>>>>> I'm not posting the program that inserts the data, but I can if that
>>>>> would be help. Thanks very much,
>>>>>
>>>>> Jack
>>>>>
>>>>
>>>
>>
>

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