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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: read repair keeps occurring on every quorum read
Date Wed, 30 Sep 2009 15:14:38 GMT
Since JIRA is mostly dead right now, here is the patch to test against 0.4.

On Mon, Sep 28, 2009 at 4:30 PM, Edmond Lau <edmond@ooyala.com> wrote:
> On Fri, Sep 25, 2009 at 8:10 PM, Jonathan Ellis <jbellis@gmail.com> wrote:
>> No, you're mixing two related concepts.
>>
>> When you do a quorum read it will fetch the actual data from one
>> replica and do digest reads from the others.  If the data from the one
>> does not match the hash from the others, then you have the
>> digestmismatchexception Edmond is seeing and read repair is performed.
>>  So this is not normal and probably a bug.
>
> Ok - I've filed a bug in jira: CASSANDRA-462.
>
>>
>> P.S. Edmund: with 2 replicas, quorum is the same as all.  So you will
>> not be able to perform reads if any node is available.  This is why
>> usually if you are going to do quorum reads you will have replication
>> factor 3 or more.
>
> Yep.  I only have 3 machines available at the moment as I'm testing
> cassandra out.
>
>>
>> -Jonathan
>>
>> On Fri, Sep 25, 2009 at 8:31 PM, Sandeep Tata <sandeep.tata@gmail.com> wrote:
>>> This is a known issue, and we should perhaps open a JIRA on it.
>>> The original Dynamo approach was to have 3 mechanisms --
>>> HintedHandoff, read-repair, and Merk trees to guarantee convergence
>>> (eventual consistency). Cassandra only has the first two. There are
>>> some corner cases where hinted-handoff alone can't be relied on to
>>> guarantee convergence which is why there's read-repair  on every read.
>>>
>>> Turning off read repair is a relatively simple (but risky) change to
>>> the code. However, minimizing unnecessary read repair is a lot
>>> trickier :)
>>>
>>>
>>> On Fri, Sep 25, 2009 at 5:39 PM, Edmond Lau <edmond@ooyala.com> wrote:
>>>> I have a 3 node cluster with a replication factor of 2, running on 0.4
>>>> RC1.  I've set both my read and write consistency levels to use a
>>>> quorum.
>>>>
>>>> I'm observing that quorum reads keep invoking read repair and log
>>>> DigestMismatchExceptions from the StorageProxy.  Obviously, this
>>>> significantly reduces my read throughput.  In the absence of any
>>>> additional inserts, I'd expect that read repair would happen at most
>>>> once before the 2 nodes responsible for the data both have fresh views
>>>> of the data.
>>>>
>>>> Here's what I see in my debug log for one machine on two consecutive
>>>> quorum reads for the data.  I get similar messages when querying any
>>>> of the 3 nodes.  Similar messages are logged on subsequent queries for
>>>> the exact same row/column.  The issue happens when reading both
>>>> supercolumns or columns.  Restarting the cluster has no effect.
>>>>
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,317 CassandraServer.java
>>>> (line 305) multiget
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,360 StorageProxy.java
>>>> (line 375) strongread reading data for
>>>> SliceByNamesReadCommand(table='Analytics', key='test',
>>>> columnParent='QueryPath(columnFamilyName='Domain',
>>>> superColumnName='null', co\
>>>> lumnName='null')', columns=[www.ooyala.com,]) from 17@172.16.130.130:7000
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,365 StorageProxy.java
>>>> (line 382) strongread reading digest for
>>>> SliceByNamesReadCommand(table='Analytics', key='test',
>>>> columnParent='QueryPath(columnFamilyName='Domain',
>>>> superColumnName='null', \
>>>> columnName='null')', columns=[www.ooyala.com,]) from 18@172.16.130.131:7000
>>>> DEBUG [ROW-READ-STAGE:1] 2009-09-26 00:26:20,380 ReadVerbHandler.java
>>>> (line 100) Read key test; sending response to
>>>> EEF5BCFF-D592-F1DE-6DEE-B74029218A29@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:1] 2009-09-26 00:26:20,387
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from EEF5BCFF-D592-F1DE-6DEE-B74029218A29@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:2] 2009-09-26 00:26:20,449
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from EEF5BCFF-D592-F1DE-6DEE-B74029218A29@172.16.130.131:7000
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,474
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,474
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>>  INFO [pool-1-thread-1] 2009-09-26 00:26:20,475 StorageProxy.java
>>>> (line 411) DigestMismatchException: test
>>>> DEBUG [ROW-READ-STAGE:2] 2009-09-26 00:26:20,477 ReadVerbHandler.java
>>>> (line 100) Read key test; sending response to 19@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:3] 2009-09-26 00:26:20,478
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from 19@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:4] 2009-09-26 00:26:20,480
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from 19@172.16.130.131:7000
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,481
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>> DEBUG [pool-1-thread-1] 2009-09-26 00:26:20,481
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>>  INFO [pool-1-thread-1] 2009-09-26 00:26:20,482
>>>> ReadResponseResolver.java (line 148) resolve: 1 ms.
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,099 CassandraServer.java
>>>> (line 305) multiget
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,100 StorageProxy.java
>>>> (line 375) strongread reading data for
>>>> SliceByNamesReadCommand(table='Analytics', key='test',
>>>> columnParent='QueryPath(columnFamilyName='Domain',
>>>> superColumnName='null', co\
>>>> lumnName='null')', columns=[www.ooyala.com,]) from 224@172.16.130.130:7000
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,100 StorageProxy.java
>>>> (line 382) strongread reading digest for
>>>> SliceByNamesReadCommand(table='Analytics', key='test',
>>>> columnParent='QueryPath(columnFamilyName='Domain',
>>>> superColumnName='null', \
>>>> columnName='null')', columns=[www.ooyala.com,]) from 225@172.16.130.131:7000
>>>> DEBUG [ROW-READ-STAGE:1] 2009-09-26 00:27:22,103 ReadVerbHandler.java
>>>> (line 100) Read key test; sending response to
>>>> CD1A7545-F759-1CA7-4D17-87FA4A16E2E4@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:1] 2009-09-26 00:27:22,103
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from CD1A7545-F759-1CA7-4D17-87FA4A16E2E4@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:2] 2009-09-26 00:27:22,107
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from CD1A7545-F759-1CA7-4D17-87FA4A16E2E4@172.16.130.131:7000
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,108
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 1
>>>> ms.
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,108
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>>  INFO [pool-1-thread-2] 2009-09-26 00:27:22,109 StorageProxy.java
>>>> (line 411) DigestMismatchException: test
>>>> DEBUG [ROW-READ-STAGE:2] 2009-09-26 00:27:22,114 ReadVerbHandler.java
>>>> (line 100) Read key test; sending response to 226@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:3] 2009-09-26 00:27:22,114
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from 226@172.16.130.130:7000
>>>> DEBUG [RESPONSE-STAGE:4] 2009-09-26 00:27:22,205
>>>> ResponseVerbHandler.java (line 34) Processing response on a callback
>>>> from 226@172.16.130.131:7000
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,206
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>> DEBUG [pool-1-thread-2] 2009-09-26 00:27:22,206
>>>> ReadResponseResolver.java (line 84) Response deserialization time : 0
>>>> ms.
>>>>  INFO [pool-1-thread-2] 2009-09-26 00:27:22,207
>>>> ReadResponseResolver.java (line 148) resolve: 1 ms.
>>>>
>>>> Thoughts?
>>>>
>>>> Edmond
>>>>
>>>
>>
>

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