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From AJ Slater ...@zuno.com>
Subject Re: Occasional 10s Timeouts on Read
Date Fri, 18 Jun 2010 17:39:30 GMT
To summarize:

If a request for a column comes in *after a period of several hours
with no requests*, then the node servicing the request hangs while
looking for its peer rather than servicing the request like it should.
It then throws either a TimedOutException or a (wrong)
NotFoundExeption.

And it doen't appear to actually send the message it says it does to
its peer. Or at least its peer doesn't report the request being
received.

And then the situation magically clears up after approximately 2 minutes.

However, if the idle period never occurs, then the problem does not
manifest. If I run a cron job with wget against my server every
minute, I do not see the problem.

I'll be looking at some tcpdump logs to see if i can suss out what's
really happening, and perhaps file this as a bug. The several hours
between reproducible events makes this whole thing aggravating for
detection, debugging and I'll assume, fixing, if it is indeed a
cassandra problem.

It was suggested on IRC that it may be my network. But gossip is
continually sending heartbeats and nodetool and the logs show the
nodes as up and available. If my network was flaking out I'd think it
would be dropping heartbeats and I'd see that.

AJ

On Thu, Jun 17, 2010 at 2:26 PM, AJ Slater <aj@zuno.com> wrote:
> These are physical machines.
>
> storage-conf.xml.fs03 is here:
>
> http://pastebin.com/weL41NB1
>
> Diffs from that for the other two storage-confs are inline here:
>
> aj@worm:../Z3/cassandra/conf/dev$ diff storage-conf.xml.lpc03
> storage-conf.xml.fs01
> 185c185
>
>>   <InitialToken>71603818521973537678586548668074777838</InitialToken>
> 229c229
> <   <ListenAddress>10.33.2.70</ListenAddress>
> ---
>>   <ListenAddress>10.33.3.10</ListenAddress>
> 241c241
> <   <ThriftAddress>10.33.2.70</ThriftAddress>
> ---
>>   <ThriftAddress>10.33.3.10</ThriftAddress>
> 341c341
> <   <ConcurrentReads>16</ConcurrentReads>
> ---
>>   <ConcurrentReads>4</ConcurrentReads>
>
>
> aj@worm:../Z3/cassandra/conf/dev$ diff storage-conf.xml.lpc03
> storage-conf.xml.fs02
> 185c185
> <   <InitialToken>0</InitialToken>
> ---
>>   <InitialToken>120215585224964746744782921158327379306</InitialToken>
> 206d205
> <       <Seed>10.33.3.20</Seed>
> 229c228
> <   <ListenAddress>10.33.2.70</ListenAddress>
> ---
>>   <ListenAddress>10.33.3.20</ListenAddress>
> 241c240
> <   <ThriftAddress>10.33.2.70</ThriftAddress>
> ---
>>   <ThriftAddress>10.33.3.20</ThriftAddress>
> 341c340
> <   <ConcurrentReads>16</ConcurrentReads>
> ---
>>   <ConcurrentReads>4</ConcurrentReads>
>
>
> Thank you for your attention,
>
> AJ
>
>
> On Thu, Jun 17, 2010 at 2:09 PM, Benjamin Black <b@b3k.us> wrote:
>> Are these physical machines or virtuals?  Did you post your
>> cassandra.in.sh and storage-conf.xml someplace?
>>
>> On Thu, Jun 17, 2010 at 10:31 AM, AJ Slater <aj@zuno.com> wrote:
>>> Total data size in the entire cluster is about twenty 12k images. With
>>> no other load on the system. I just ask for one column and I get these
>>> timeouts. Performing multiple gets on the columns leads to multiple
>>> timeouts for a period of a few seconds or minutes and then the
>>> situation magically resolves itself and response times are down to
>>> single digit milliseconds for a column get.
>>>
>>> On Thu, Jun 17, 2010 at 10:24 AM, AJ Slater <aj@zuno.com> wrote:
>>>> Cassandra 0.6.2 from the apache debian source.
>>>> Ubunutu Jaunty. Sun Java6 jvm.
>>>>
>>>> All nodes in separate racks at 365 main.
>>>>
>>>> On Thu, Jun 17, 2010 at 10:12 AM, AJ Slater <aj@zuno.com> wrote:
>>>>> I'm seing 10s timeouts on reads few times a day. Its hard to reproduce
>>>>> consistently but seems to happen most often after its been a long time
>>>>> between reads. After presenting itself for a couple minutes the
>>>>> problem then goes away.
>>>>>
>>>>> I've got a three node cluster with replication factor 2, reading at
>>>>> consistency level ONE. The columns being read are around 12k each. The
>>>>> nodes are 8GB multicore boxes with the JVM limits between 4GB and 6GB.
>>>>>
>>>>> Here's an application log from early this morning when a developer in
>>>>> Belgrade accessed the system:
>>>>>
>>>>> Jun 17 03:54:17 lpc03 pinhole[5736]: MainThread:pinhole.py:61 |
>>>>> Requested image_id: 5827067133c3d670071c17d9144f0b49
>>>>> Jun 17 03:54:27 lpc03 pinhole[5736]: MainThread:pinhole.py:76 |
>>>>> TimedOutException for Image 5827067133c3d670071c17d9144f0b49
>>>>> Jun 17 03:54:27 lpc03 pinhole[5736]: MainThread:zlog.py:105 | Image
>>>>> Get took 10005.388975 ms
>>>>> Jun 17 03:54:27 lpc03 pinhole[5736]: MainThread:pinhole.py:61 |
>>>>> Requested image_id: af8caf3b76ce97d13812ddf795104a5c
>>>>> Jun 17 03:54:27 lpc03 pinhole[5736]: MainThread:zlog.py:105 | Image
>>>>> Get took 3.658056 ms
>>>>> Jun 17 03:54:27 lpc03 pinhole[5736]: MainThread:zlog.py:105 | Image
>>>>> Transform took 0.978947 ms
>>>>>
>>>>> That's a Timeout and then a successful get of another column.
>>>>>
>>>>> Here's the cassandra log for 10.33.2.70:
>>>>>
>>>>> DEBUG 03:54:17,070 get_slice
>>>>> DEBUG 03:54:17,071 weakreadremote reading
>>>>> SliceFromReadCommand(table='jolitics.com',
>>>>> key='5827067133c3d670071c17d9144f0b49',
>>>>> column_parent='QueryPath(columnFamilyName='Images',
>>>>> superColumnName='null', columnName='null')', start='', finish='
>>>>> ', reversed=false, count=100)
>>>>> DEBUG 03:54:17,071 weakreadremote reading
>>>>> SliceFromReadCommand(table='jolitics.com',
>>>>> key='5827067133c3d670071c17d9144f0b49',
>>>>> column_parent='QueryPath(columnFamilyName='Images',
>>>>> superColumnName='null', columnName='null')', start='', finish='
>>>>> ', reversed=false, count=100) from 45138@/10.33.3.10
>>>>> DEBUG 03:54:27,077 get_slice
>>>>> DEBUG 03:54:27,078 weakreadlocal reading
>>>>> SliceFromReadCommand(table='jolitics.com',
>>>>> key='af8caf3b76ce97d13812ddf795104a5c',
>>>>> column_parent='QueryPath(columnFamilyName='Images',
>>>>> superColumnName='null', columnName='null')', start='', finish=''
>>>>> , reversed=false, count=100)
>>>>> DEBUG 03:54:27,079 collecting body:false:1610@1275951327610885
>>>>> DEBUG 03:54:27,080 collecting body:false:1610@1275951327610885
>>>>> DEBUG 03:54:27,080 Reading consistency digest for af8caf3b76ce97d13812ddf795104a
>>>>> 5c from 45168@[/10.33.2.70, /10.33.3.10]
>>>>> DEBUG 03:54:50,779 Disseminating load info ...
>>>>>
>>>>> It looks like it asks for key='5827067133c3d670071c17d9144f0b49' from
>>>>> the local host and also queries 10.33.3.10 for the first one and then
>>>>> for 'af8caf3b76ce97d13812ddf795104a5c' it only queries the local host
>>>>> and then returns appropriately.
>>>>>
>>>>> Here's the log for 10.33.3.10 around that time:
>>>>>
>>>>> DEBUG 03:54:19,645 Disseminating load info ...
>>>>> DEBUG 03:55:19,645 Disseminating load info ...
>>>>> DEBUG 03:56:19,646 Disseminating load info ...
>>>>> DEBUG 03:57:19,645 Disseminating load info ...
>>>>> DEBUG 03:58:19,645 Disseminating load info ...
>>>>> DEBUG 03:59:19,646 Disseminating load info ...
>>>>> DEBUG 04:00:18,635 GC for ParNew: 4 ms, 21443128 reclaimed leaving
>>>>> 55875144 used; max is 6580535296
>>>>>
>>>>> No record of communication from 10.33.2.70.
>>>>>
>>>>> Does this ring any bells for anyone? I can of course attach
>>>>> storage-conf's for all nodes if that sounds useful and I'll be on
>>>>> #cassandra as ajslater.
>>>>>
>>>>> Much thanks for taking a look and any suggestions. We fear we'll have
>>>>> to abandon Cassandra if this bug cannot be resolved.
>>>>>
>>>>> AJ
>>>>>
>>>>
>>>
>>
>

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