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From Abraham Sanderson <asander...@lingotek.com>
Subject Re: Problems with subcolumn retrieval after upgrade from 0.6 to 0.7
Date Mon, 18 Apr 2011 21:26:54 GMT
I wish it were consistent enough that the answer were simple...  It varies
between just the requested subcolumn to all subcolumns.  It always does
return the columns in order, and the requested column is always one of the
columns returned.   However, the slice start is not consistently in the same
place(like n+1 or n-1).  For example, if I have CF['key']['supercolumn'
['a','b','c','d','e']], and query for 'c', sometimes i get a slice with 'a',
'b', 'c', other times its 'b', 'c', 'd', sometimes 'c', 'd'.  When the
column name is closer to the end of the range('d' or 'e'), sometimes it
justs a slice with the column.  The sporadic behavior makes me think that
it's a race condition, but the behavior linked to the column range makes we
think I'm overrunning the buffer somewhere.  I at first suspected that I was
inadvertently making modifications to the buffers in application code during
serialization/deserialization, so I did the tests in the cli.  This limits
it to just cassandra/thrift code and my custom types.  Am I missing some
other factor?  While debugging I have noticed that the byte buffers contain
more than they used to; it looks to me like tokens that contain parts of the
thrift response.  I'd see strings like
"???get_slice???Foo??7c2f5d5b-b370-42e1-a6a2-77fc721440fe????"  Is it
possible that I am inadvertently using a reserved token or something on my
supercolumn name and this is screwing with the slice command?

Abe

On Mon, Apr 18, 2011 at 2:55 PM, aaron morton <aaron@thelastpickle.com>wrote:

> When you run the get_slice which columns are returned ?
>
>
> Aaron
>
> On 19 Apr 2011, at 04:12, Abraham Sanderson wrote:
>
> Ok, I made the changes and tried again.  Here is the before modifying my
> method using a simple get, confirmed the same output in the cli:
>
> DEBUG [pool-1-thread-2] 2011-04-18 09:37:23,910 CassandraServer.java (line
> 279) get
> DEBUG [pool-1-thread-2] 2011-04-18 09:37:23,911 StorageProxy.java (line
> 322) Command/ConsistencyLevel is SliceByNamesReadCommand(table='DocStore',
> key=64316337663662392d313432352d346661622d623037342d353537346335346361653038,
> columnParent='QueryPath(columnFamilyName='Tran
> slationsByTarget', superColumnName='java.nio.HeapByteBuffer[pos=95 lim=211
> cap=244]', columnName='null')',
> columns=[7c2f5d5b-b370-42e1-a6a2-77fc721440fe,])/ALL
> DEBUG [pool-1-thread-2] 2011-04-18 09:37:23,911 ReadCallback.java (line 84)
> Blockfor/repair is 1/true; setting up requests to localhost/127.0.0.1
> DEBUG [pool-1-thread-2] 2011-04-18 09:37:23,911 StorageProxy.java (line
> 345) reading data locally
> DEBUG [ReadStage:4] 2011-04-18 09:37:23,911 StorageProxy.java (line 450)
> LocalReadRunnable reading SliceByNamesReadCommand(table='DocStore',
> key=64316337663662392d313432352d346661622d623037342d353537346335346361653038,
> columnParent='QueryPath(columnFamilyName='Translatio
> nsByTarget', superColumnName='java.nio.HeapByteBuffer[pos=95 lim=211
> cap=244]', columnName='null')',
> columns=[7c2f5d5b-b370-42e1-a6a2-77fc721440fe,])
> DEBUG [pool-1-thread-2] 2011-04-18 09:37:23,912 StorageProxy.java (line
> 395) Read: 1 ms.
> ERROR [pool-1-thread-2] 2011-04-18 09:37:23,912 Cassandra.java (line 2665)
> Internal error processing get
> java.lang.AssertionError
>         at
> org.apache.cassandra.thrift.CassandraServer.get(CassandraServer.java:300)
>         at
> org.apache.cassandra.thrift.Cassandra$Processor$get.process(Cassandra.java:2655)
>         at
> org.apache.cassandra.thrift.Cassandra$Processor.process(Cassandra.java:2555)
>         at
> org.apache.cassandra.thrift.CustomTThreadPoolServer$WorkerProcess.run(CustomTThreadPoolServer.java:206)
>         at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
>         at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
>         at java.lang.Thread.run(Thread.java:636)
>
> And here is the after...it succeeds here but still gives me multiple
> subcolumns in the response.  Same behavior, it seems, I'm just sidestepping
> the original AssertionError:
>
> DEBUG [pool-1-thread-6] 2011-04-18 09:50:26,617 CassandraServer.java (line
> 232) get_slice
> DEBUG [pool-1-thread-6] 2011-04-18 09:50:26,617 StorageProxy.java (line
> 322) Command/ConsistencyLevel is SliceByNamesReadCommand(table='DocStore',
> key=64316337663662392d313432352d346661622d623037342d353537346335346361653038,
> columnParent='QueryPath(columnFamilyName='TranslationsByTarget',
> superColumnName='java.nio.HeapByteBuffer[pos=101 lim=217 cap=259]',
> columnName='null')', columns=[7c2f5d5b-b370-42e1-a6a2-77fc721440fe,])/ALL
> DEBUG [pool-1-thread-6] 2011-04-18 09:50:26,617 ReadCallback.java (line 84)
> Blockfor/repair is 1/true; setting up requests to localhost/127.0.0.1
> DEBUG [pool-1-thread-6] 2011-04-18 09:50:26,617 StorageProxy.java (line
> 345) reading data locally
> DEBUG [ReadStage:3] 2011-04-18 09:50:26,618 StorageProxy.java (line 450)
> LocalReadRunnable reading SliceByNamesReadCommand(table='DocStore',
> key=64316337663662392d313432352d346661622d623037342d353537346335346361653038,
> columnParent='QueryPath(columnFamilyName='TranslationsByTarget',
> superColumnName='java.nio.HeapByteBuffer[pos=101 lim=217 cap=259]',
> columnName='null')', columns=[7c2f5d5b-b370-42e1-a6a2-77fc721440fe,])
> DEBUG [pool-1-thread-6] 2011-04-18 09:50:26,618 StorageProxy.java (line
> 395) Read: 0 ms.
>
> My comparators are relatively simple.  Basically I have a schema that
> required heterogenous columns, but I needed to be able to deserialize them
> in unique ways.  So there is always a type byte that precedes the bytes of
> the data.  The supercolumn in this case is a general data type, which
> happens to represent a serializable object:
>
>   public void validate(ByteBuffer bytes)
>     throws MarshalException
>   {
>     if(bytes.remaining() == 0)
>       return;
>
>     validateDataType(bytes.get(bytes.position()));
>     return;
>   }
>
>   public int compare(ByteBuffer bytes1, ByteBuffer bytes2)
>   {
>     if (bytes1.remaining() == 0)
>       return bytes2.remaining() == 0 ? 0 : -1;
>     else if (bytes2.remaining() == 0)
>       return 1;
>     else
>     {
>       // compare type
> bytes
>
>       byte T1 = bytes1.get(bytes1.position());
>       byte T2 = bytes2.get(bytes2.position());
>       if (T1 != T2)
>         return (T1 - T2);
>
>       // compare
> values
>
>       return ByteBufferUtil.compareUnsigned(bytes1, bytes2);
>     }
>   }
>
> The subcolumn is similar...just a UUID with a type byte prefix:
>
>   public void validate(ByteBuffer bytes)
>     throws MarshalException
>   {
>     if(bytes.remaining() == 0)
>       return;
>
>     validateDataType(bytes.get(bytes.position()));
>     if((bytes.remaining() - 1) == 0)
>       return;
>     else if((bytes.remaining() - 1) != 16)
>       throw new MarshalException("UUID value must be exactly 16 bytes");
>   }
>
>   public int compare(ByteBuffer bytes1, ByteBuffer bytes2)
>   {
>     if (bytes1.remaining() == 0)
>       return bytes2.remaining() == 0 ? 0 : -1;
>     else if (bytes2.remaining() == 0)
>       return 1;
>     else
>     {
>       // compare type
> bytes
>
>       byte T1 = bytes1.get(bytes1.position());
>       byte T2 = bytes2.get(bytes2.position());
>       if (T1 != T2)
>         return (T1 - T2);
>
>       // compare
> values
>
>       UUID U1 = getUUID(bytes1, bytes1.position()+1);
>       UUID U2 = getUUID(bytes2, bytes2.position()+1);
>       return U1.compareTo(U2);
>     }
>   }
>
>   static UUID getUUID(ByteBuffer bytes, int pos)
>   {
>     long msBits = bytes.getLong(pos);
>     long lsBits = bytes.getLong(pos+8);
>     return new UUID(msBits, lsBits);
>   }
>
> All of my buffer reads are done by index, the position shouldn't be
> changing at all.
>
> Abe Sanderson
>
> On Sat, Apr 16, 2011 at 5:38 PM, aaron morton <aaron@thelastpickle.com>wrote:
>
>> Can you run the same request as a get_slice naming the column in the
>> SlicePredicate and see what comes back ?
>>
>> Can you reproduce the fault with logging set at DEBUG and send the logs ?
>>
>> Also, whats the compare function like for your custom type ?
>>
>> Cheers
>> Aaron
>>
>>
>> On 16 Apr 2011, at 07:34, Abraham Sanderson wrote:
>>
>> > I'm having some issues with a few of my ColumnFamilies after a cassandra
>> upgrade/import from 0.6.1 to 0.7.4.  I followed the instructions to upgrade
>> and everything seem to work OK...until I got into the application and
>> noticed some wierd behavior.  I was getting the following stacktrace in
>> cassandra occassionally when I did get operations for a single subcolumn for
>> some of the Super type CFs:
>> >
>> > ERROR 12:56:05,669 Internal error processing get
>> > java.lang.AssertionError
>> >         at org.apache.cassandra.thrift.
>> > CassandraServer.get(CassandraServer.java:300)
>> >         at
>> org.apache.cassandra.thrift.Cassandra$Processor$get.process(Cassandra.java:2655)
>> >         at
>> org.apache.cassandra.thrift.Cassandra$Processor.process(Cassandra.java:2555)
>> >         at
>> org.apache.cassandra.thrift.CustomTThreadPoolServer$WorkerProcess.run(CustomTThreadPoolServer.java:206)
>> >         at
>> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
>> >         at
>> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
>> >         at java.lang.Thread.run(Thread.java:636)
>> >
>> > The assertion that is failing is the check that only one column is
>> retrieved by the get.  I did some debugging with the cli and a remote
>>  debugger and found a few interesting patterns.  First, the problem does not
>> seem consistently duplicatable.  If one supercolumn is affected though, it
>> will happen more frequently for subcolumns that when sorted appear at the
>> beginning of the range.  For columns near the end of the range, it seems to
>> be more intermittent, and almost never occurs when I step through the code
>> line by line.  The only factor I can think of that might cause issues is
>> that I am using custom data types for all supercolumns and columns.  I
>> originally thought I might be reading past the end of the ByteBuffer, but I
>> have quadrupled checked that this is not the case.
>> >
>> > Abe Sanderson
>>
>>
>
>

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