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From Edmond Lau <edm...@ooyala.com>
Subject Re: repeated timeouts on quorum reads
Date Thu, 22 Oct 2009 00:33:18 GMT
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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