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From Philippe <watche...@gmail.com>
Subject Re: Unable to repair a node
Date Tue, 16 Aug 2011 22:09:51 GMT
One last thought : what happens when you ctrl-c a nodetool repair ? Does it
stop the repair on the server ? If not, then I think I have multiple repairs
still running. Is there any way to check this ?

Thanks

2011/8/16 Philippe <watcherfr@gmail.com>

> Even more interesting behavior : a repair on a CF has consequences on other
> CFs. I didn't expect that.
>
> There are no writes being issued to the cluster yet the logs indicate that
>
>    - SSTableReader has opened dozens and dozens of files, most of them
>    unrelated to the CF being repaired
>    - compactions are taking place continuously on CFs other than the one
>    being repaired, even CFs in other keyspaces
>    - I see "Sending AEService tree" messages for CF not being repaired.
>
>
> After a very long time, I got some AES messages indicating that streaming
> from node C had finished and then many minutes after that node B. And yet
> the pending stream count on node B hasn't changed.
>
> The *-data.db files for the CF being repaired are about 70MB on-disk.
>
> Maybe when a stream is fully received on node B, netstats indicates that no
> streams are pending but since they are not acknowledged, node A doesn't ?
>
>
> 2011/8/16 Philippe <watcherfr@gmail.com>
>
>> I'm still trying different stuff. Here are my latest findings, maybe
>> someone will find them useful:
>>
>>    - I have been able to repair some small column families by issuing a
>>    repair [KS] [CF]. When testing on the ring with no writes at all, it still
>>    takes about 2 repairs to get "consistent" logs for all AES requests.
>>    - Launching a repair one the smallest CF of the biggest KS has
>>    triggered a flurry of compactions and streams. Some of those streams are for
>>    other CF in that keyspace !?
>>    - During repairs (one at a time cluster-wide), I get 25-50% io waits &
>>    35%-50% cpu usage on a 6 core SATA-disk setup
>>
>> What is surprising to me (bug?) is that netstats shows me streams going
>> from node A to node B at 0% progress. But netstats on node B doesn't show me
>> any streams coming in. I'm thinking that repairs may be never ending and
>> that may be messing up my compactions hence the huge pile up of compactions
>> until the disk fulls.
>> I know there's an issue related to failed streams & repairs, could I be
>> hitting it ?
>>
>> Thanks
>>
>> 2011/8/14 Philippe <watcherfr@gmail.com>
>>
>>> @Teijo : thanks for the procedure, I hope I won't have to do that
>>>
>>> Peter, I'll answer inline. Thanks for the detailed answer.
>>>
>>>
>>>>  > the number of SSTables for some keyspaces goes dramatically up (from
>>>> 3 or 4
>>>> > to several dozens).
>>>>
>>>> Typically with a long running compaction, such as that triggered by
>>>> repair, that's what happens as flushed memtables accumulate. In
>>>> particular for memtables with frequent flushes.
>>>>
>>>> Are you running with concurrent compaction enabled?
>>>>
>>> Yes, it is enabled. On my 0.8 cluster, cassandra.yaml has this (it's
>>> commented). BTW, I have 6 cores on each server.
>>>
>>> #concurrent_compactors: 1
>>>
>>> > the commit log keeps increasing in size, I'm at 4.3G now, it went up to
>>>> 40G
>>>> > when the compaction was throttled at 16MB/s. On the other nodes it's
>>>> around
>>>> > 1GB at most
>>>> Hmmmm. The Commit Log should not be retained longer than what is
>>>> required for memtables to be flushed. Is it possible you have had an
>>>> out-of-disk condition and flushing has stalled? Are you seeing flushes
>>>> happening in the log?
>>>>
>>> No I don't believe there was ever an out of disk.  Yes it is flushing for
>>> the first couple of hours.
>>> Then, when repair seems locked up, my log is mostly filled with lines
>>> such as this
>>> INFO [ScheduledTasks:1] 2011-08-14 23:15:47,267 StatusLogger.java (line
>>> 88) [My_Keyspace].[My_Columnfamily]           45,105541               50/50
>>>               20/20
>>>  Why is that ?
>>>
>>> > the data directory is bigger than on the other nodes. I've seen it go
>>>> up to
>>>> > 480GB when the compaction was throttled at 16MB/s
>>>> How much data are you writing? Is it at all plausible that the huge
>>>> spike is a reflection of lots of overwriting writes that aren't being
>>>> compacted?
>>>>
>>> No, there's no bulk loading going on at the moment and I'm pretty sure
>>> there wasn't when it spiked up to that load.
>>> I've never measured the load because it's a mix of counter increments and
>>> new counters all the time. It's not that much though.
>>>
>>>
>>>> Normally when disk space spikes with repair it's due to other nodes
>>>> streaming huge amounts (maybe all of their data) to the node, leading
>>>> to a temporary spike. But if your "real" size is expected to be 60,
>>>> 480 sounds excessive. Are you sure other nodes aren't running repairs
>>>> at the same time and magnifying each other's data load spikes?
>>>>
>>> Yes, the two other nodes were running repairs. I had them scheduled at 8
>>> hour intervals but they must have started.
>>> When data is streamed from one to another, does that data go into the
>>> commit log as a regular write ?
>>>  How much of a negative impact can that have on the repair going on on
>>> this node ?
>>>
>>> > What's even weirder is that currently I have 9 compactions running but
>>>> CPU
>>>> > is throttled at 1/number of cores half the time (while > 80% the
rest
>>>> of the
>>>> > time). Could this be because other repairs are happening in the ring
?
>>>> You mean compaction is taking less CPU than it "should"?
>>>>
>>> Yes
>>>
>>>
>>>> No, this should not be due to other nodes repairing. However it sounds
>>>> to me like you are bottlenecking on I/O and the repairs and
>>>>
>>> Yes, I/O is really high on the node right now. Around 50% I/O waits.
>>>
>>>
>>>> compactions are probably proceeding extremely slowly, probably being
>>>> completely drowned out by live traffic (which is probably having an
>>>> abnormally high performance impact due to data size spike).
>>>>
>>> Yes, the live traffic is 3 to 10x times slower during repair. Ouch... I
>>> hope I won't to do this too often while in production !
>>>
>>>
>>>>
>>>> What's your read concurrency configured on the node? What does "iostat
>>>> -x -k 1" show in the average queue size column?
>>>
>>> Average queue size on the disk (RAID-1 + separate LVM volumes for data,
>>> commit log, caches, logs)) varies between 2 and 90. I'd say the average is
>>> around 30-40. Very high variation.
>>>
>>>
>>>> Is "nodetool -h
>>>> localhost tpstats" showing that ReadStage is usually "full" (@ your
>>>> limit)?
>>>>
>>> No backlog at all in tpstats
>>>
>>> I've figured out how AES is logging its actions and it looks like it
>>> really is going through every CF in every keyspace and doing a tree request
>>> for every token range
>>> So it really looks like it's just taking forever to compact stuff as it's
>>> repairing.
>>> I saw in another email that repairing was taking 2-3mn/ GB... it looks
>>> like a lot more for my ring. Anybody else have numbers ?
>>>
>>> Thanks
>>>
>>
>>
>

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