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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: repeated timeouts on quorum reads
Date Thu, 22 Oct 2009 14:42:25 GMT
What is your columnfamily definition?  What query should I test with?

On Wed, Oct 21, 2009 at 7:33 PM, Edmond Lau <edmond@ooyala.com> wrote:
> On Tue, Oct 20, 2009 at 2:03 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> Okay, so we have 2 problems:
>>
>>  - the read is simply too slow
>>  - we're doing unnecessary(?) read repairs
>>
>> For the first I think it's going to be easiest if you can export the
>> row in question so we can do some profiling.  (Eric will have a tool
>> to do this soon.)
>
> Ok - I've created a cassandra setup with just the row in question and
> tarred up the data + storage-conf.xml for the three nodes:
>
> http://demo.ooyala.com/cassandra/cassandra-1.tgz
> http://demo.ooyala.com/cassandra/cassandra-2.tgz
> http://demo.ooyala.com/cassandra/cassandra-3.tgz
>
>>
>> For the second, how sure are you that the repair is unnecessary?  Does
>> it repeat the repair when you do the query again after letting the
>> callbacks complete?
>
> I didn't do any writes as I was debugging the issue whereas I was
> reading the same data a whole bunch of times, so the repair should've
> been unnecessary.
>
> Thanks for your help,
> Edmond
>
>>
>> -Jonathan
>>
>> On Mon, Oct 19, 2009 at 11:38 PM, Edmond Lau <edmond@ooyala.com> wrote:
>>> A single local read with debug logging takes 3-4 secs on the node with
>>> 3 data files.  It actually takes roughly as long on the other nodes as
>>> well (I was incorrect in saying that they were fast).
>>>
>>> DEBUG [pool-1-thread-22] 2009-10-20 04:26:06,953 CassandraServer.java
>>> (line 219) get_slice
>>> DEBUG [pool-1-thread-22] 2009-10-20 04:26:06,955 StorageProxy.java
>>> (line 468) weakreadlocal reading
>>> SliceFromReadCommand(table='Analytics', key='o:movie',
>>> column_parent='QueryPath(columnFamilyName='movie',
>>> superColumnName='[B@26e00675', columnName='null')', start='',
>>> finish='', reversed=false, count=1)
>>> DEBUG [pool-1-thread-22] 2009-10-20 04:26:10,382 SliceQueryFilter.java
>>> (line 115) collecting 1000036:false:515@1255978226411394
>>> DEBUG [CONSISTENCY-MANAGER:2] 2009-10-20 04:26:10,383
>>> ConsistencyManager.java (line 168) Reading consistency digest for
>>> o:movie from 2926@[172.16.129.71:7000, 172.16.129.72:7000]
>>> DEBUG [RESPONSE-STAGE:1] 2009-10-20 04:26:13,332
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 2926@172.16.129.71:7000
>>> DEBUG [RESPONSE-STAGE:3] 2009-10-20 04:26:13,675
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 2926@172.16.129.72:7000
>>> DEBUG [RESPONSE-STAGE:3] 2009-10-20 04:26:13,677
>>> ConsistencyManager.java (line 96) Performing read repair for o:movie
>>> to 2937@[172.16.129.71:7000, 172.16.129.72:7000, 172.16.129.75:7000]
>>>
>>> Also, it's unclear why there's a read repair going on above, since I
>>> haven't made any updates.
>>>
>>> Doing a quorum read on the node with 3 data files takes 7 seconds w/
>>> debug logging and leads to a DigestMismatchException, again even
>>> though I haven't made any updates.
>>>
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:00,892 CassandraServer.java
>>> (line 219) get_slice
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:00,894 StorageProxy.java
>>> (line 374) strongread reading data for
>>> SliceFromReadCommand(table='Analytics', key='o:movie',
>>> column_parent='QueryPath(columnFamilyName='movie',
>>> superColumnName='[B@2cf50c5f', columnName='null')', start='',
>>> finish='', reversed=false, count=1) from 3675@172.16.129.75:7000
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:00,894 StorageProxy.java
>>> (line 381) strongread reading digest for
>>> SliceFromReadCommand(table='Analytics', key='o:movie',
>>> column_parent='QueryPath(columnFamilyName='movie',
>>> superColumnName='[B@2cf50c5f', columnName='null')', start='',
>>> finish='', reversed=false, count=1) from 3676@172.16.129.71:7000
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:00,895 StorageProxy.java
>>> (line 381) strongread reading digest for
>>> SliceFromReadCommand(table='Analytics', key='o:movie',
>>> column_parent='QueryPath(columnFamilyName='movie',
>>> superColumnName='[B@2cf50c5f', columnName='null')', start='',
>>> finish='', reversed=false, count=1) from 3676@172.16.129.72:7000
>>> DEBUG [RESPONSE-STAGE:3] 2009-10-20 04:30:03,994
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 15445226-F6EF-C97B-F239-FC0316748C5E@172.16.129.71:7000
>>> DEBUG [RESPONSE-STAGE:2] 2009-10-20 04:30:04,107
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 15445226-F6EF-C97B-F239-FC0316748C5E@172.16.129.72:7000
>>> DEBUG [ROW-READ-STAGE:9] 2009-10-20 04:30:04,787 SliceQueryFilter.java
>>> (line 115) collecting 1000036:false:515@1255978226411394
>>> DEBUG [ROW-READ-STAGE:9] 2009-10-20 04:30:04,788 ReadVerbHandler.java
>>> (line 100) Read key o:movie; sending response to
>>> 15445226-F6EF-C97B-F239-FC0316748C5E@172.16.129.75:7000
>>> DEBUG [RESPONSE-STAGE:4] 2009-10-20 04:30:04,788
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 15445226-F6EF-C97B-F239-FC0316748C5E@172.16.129.75:7000
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:04,789
>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>> ms.
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:04,790
>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>> ms.
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:04,791
>>> ReadResponseResolver.java (line 84) Response deserialization time : 1
>>> ms.
>>>  INFO [pool-1-thread-25] 2009-10-20 04:30:04,792 StorageProxy.java
>>> (line 410) DigestMismatchException: o:movie
>>> DEBUG [RESPONSE-STAGE:1] 2009-10-20 04:30:07,953
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 3690@172.16.129.71:7000
>>> DEBUG [RESPONSE-STAGE:3] 2009-10-20 04:30:08,130
>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>> from 3690@172.16.129.72:7000
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:08,132
>>> ReadResponseResolver.java (line 84) Response deserialization time : 1
>>> ms.
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:08,132
>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>> ms.
>>> DEBUG [pool-1-thread-25] 2009-10-20 04:30:08,132
>>> ReadResponseResolver.java (line 149) resolve: 1 ms.
>>> DEBUG [ROW-READ-STAGE:10] 2009-10-20 04:30:08,235
>>> SliceQueryFilter.java (line 115) collecting
>>> 1000036:false:515@1255978226411394
>>> DEBUG [ROW-READ-STAGE:10] 2009-10-20 04:30:08,235 ReadVerbHandler.java
>>> (line 100) Read key o:movie; sending response to
>>> 3690@172.16.129.75:7000
>>>
>>> Edmond
>>>
>>> On Mon, Oct 19, 2009 at 8:04 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>>>> On Mon, Oct 19, 2009 at 9:48 PM, Edmond Lau <edmond@ooyala.com> wrote:
>>>>> 8 data files total.  3 nodes have 1, 1 has 2, the 3rd has 3.
>>>>>
>>>>>> Does it still take ~8s if you direct a CL.ONE query at one of the
>>>>>> nodes you know has the data (i.e., a local read)?
>>>>>
>>>>> Local reads return quickly, but if you look at the logs below, there's
>>>>> 6 secs from when cassandra prints that it's reading a consistency
>>>>> digest to when it processes a callback.
>>>>
>>>> That's from when it sends the digest command, to when it gets a callback.
>>>>
>>>> Something doesn't add up.  If computing &sending a digest response
>>>> takes 6s, either reading the row or computing the digest must be
>>>> taking substantial time.  But if local reads are fast, it's not
>>>> reading the row that is slow, and if resolve is fast (from your logs,
>>>> it is 2ms) then it's not computing the digest that is slow.
>>>>
>>>> Try doing a local read from the node with 3 data files, see if that is slower.
>>>>
>>>> If you still see a fast read there, add some more debug logging in
>>>> ReadVerbHandler.java, where it says something like (I'm going from
>>>> trunk here but 0.4.1 is similar)
>>>>
>>>>            Row row = readCommand.getRow(table);
>>>>            ReadResponse readResponse;
>>>>            if (readCommand.isDigestQuery())
>>>>            {
>>>>                readResponse = new ReadResponse(row.digest());
>>>>
>>>> time the getRow and the row.digest() calls and log how long those take
>>>> in the quorum scenario.
>>>>
>>>> -Jonathan
>>>>
>>>
>>
>

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