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From Edmond Lau <edm...@ooyala.com>
Subject Re: repeated timeouts on quorum reads
Date Thu, 22 Oct 2009 15:59:07 GMT
Try:

keyspace: "Analytics"
key: "o:movie"
column family: "movie"
super column: "all"

I was able to get timeouts with a few concurrent get_slice() calls
(3-4 with debug logging, 6 without) on the super column, with start =
"", finish = "", and count = 1.

Edmond

On Thu, Oct 22, 2009 at 7:42 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
> 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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