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From David Hawthorne <dha...@gmx.3crowd.com>
Subject Re: ReplicateOnWrite issues
Date Tue, 12 Jul 2011 07:37:42 GMT
It's definitely for counters, and some of the rows I'm inserting are long-ish, if 1.3MB is
long.

Maybe it would help if I said I was using counter super columns.  I'm also writing to only
a handful of rows at a time, until they are full.  It looks like the counter super column
code in addReadCommandFromColumnFamily, in the ReplicateOnWrite handling, might not be optimized
for this kind of load.

It looks like I may be able to turn off replicate_on_write for the CFs as long as I use CL.ONE
to get around this in the short term, but I'd like to know what happens when replicate on
write is true and when it is false so I can make a more informed choice.

On Jul 12, 2011, at 12:20 AM, Yang wrote:

> interesting,
> 
> first just to make sure: since replicateOnWrite is for Counters, you
> are using counters (you use the word "insert" instead of
> "add/increment" ) right?
> 
> if you are using counters, supposedly the leader runs
> replicateOnWrite, somehow all your adds find the one box as leader,
> that's probably something worth investigating.
> 
> finally, u could try debugging into those replicateOnWrite tasks and
> see what they are doing exactly, maybe there is something immediately
> wrong
> 
> 
> 
> On Mon, Jul 11, 2011 at 11:57 PM, David Hawthorne <dhawth@gmx.3crowd.com> wrote:
>> This is now my fourth attempt to get the message through.  Apologies if you see multiple
copies.
>> 
>> I've tried to give as much relevant data as I can think of, but please let me know
if you need any other info.  I spent the day getting jmxtrans to talk to statsd with the cassandra
JMX data, so I can provide graphs of just about anything you want.  I can also re-run the
tests to replicate the problem if need be.  As always, thanks for taking a look!
>> 
>> I have a 4 host test cluster that I'm writing counters into running 0.8.1, and I'm
writing to it with hector with CL.ONE or CL.QUORUM (test was run with each and both gave the
same results).  Partitioner is the RandomPartitioner, and RF=3.  nodetool ring shows that
actual data is well balanced:
>> 
>> Address         DC          Rack        Status State   Load            Owns    Token
>>                                                                              127605887595351923798765477786913079296
>> 10.0.0.57    datacenter1 rack1       Up     Normal  1.59 GB         25.00%  0
>> 10.0.0.56    datacenter1 rack1       Up     Normal  1.39 GB         25.00%  42535295865117307932921825928971026432
>> 10.0.0.55    datacenter1 rack1       Up     Normal  1.24 GB         25.00%  85070591730234615865843651857942052864
>> 10.0.0.54    datacenter1 rack1       Up     Normal  1.34 GB         25.00%  127605887595351923798765477786913079296
>> 
>> I also tested against a 1-box test cluster with RF=1.
>> 
>> Both show the same results:  high performance for a while, and then ReplicateOnWrite
backs way up (I've seen it as high as a million), the cassandra process becomes unresponsive,
and the hector client starts throwing exceptions.  High performance in this case equates to
about 5-20k inserts/sec on both the 4-box and 1-box cluster (I'm inserting one long row at
a time, so the performance is bounded by the one box owning the row).  The cassandra process
never seems to recover, even if left for 24 hours.  It's still chewing through those ReplicateOnWrite
pending tasks.
>> 
>> GC doesn't seem to be a factor.  Logs show GCs completing in < 1s on all 4 boxes
in the test cluster, as well as on the 1 standalone server.
>> 
>> I'm also seeing highly erratic performance from the cluster in general:  inserts/sec
usually start at around 3k, but then maybe creep up towards 6k, then drop back down to below
1k for an extended period of time, then maybe 1% of the time they'll spike up to 8k or even
15k, but that doesn't last more than 30 seconds.
>> 
>> Here's the tpstats output from all 4 boxes:
>> 
>> Slowest/most problematic/highest cpu usage one:
>> 
>> This tpstats output is also representative of the one box cluster about 20 minutes
into my insert run.
>> 
>> 4 $ ./nodetool -h localhost tpstats
>> Pool Name                    Active   Pending      Completed
>> ReadStage                         0         0              0
>> RequestResponseStage              0         0       59095840
>> MutationStage                     0         0       31182942
>> ReadRepairStage                   0         0              0
>> ReplicateOnWriteStage            32    928042       28246716
>> GossipStage                       1         1         449464
>> AntiEntropyStage                  0         0              0
>> MigrationStage                    0         0              4
>> MemtablePostFlusher               0         0            445
>> StreamStage                       0         0              0
>> FlushWriter                       0         0            445
>> FILEUTILS-DELETE-POOL             0         0             38
>> MiscStage                         0         0              0
>> FlushSorter                       0         0              0
>> InternalResponseStage             0         0              4
>> HintedHandoff                     0         0              0
>> 
>> Second highest cpu usage one:
>> 
>> 3 $ ./nodetool -h localhost tpstats
>> Pool Name                    Active   Pending      Completed
>> ReadStage                         0         0              0
>> RequestResponseStage              0         0       27413910
>> MutationStage                     0         0       27523094
>> ReadRepairStage                   0         0              0
>> ReplicateOnWriteStage             0         0       11111971
>> GossipStage                       0         0         335422
>> AntiEntropyStage                  0         0              0
>> MigrationStage                    0         0              4
>> MemtablePostFlusher               0         0             66
>> StreamStage                       0         0              0
>> FlushWriter                       0         0             66
>> FILEUTILS-DELETE-POOL             0         0             31
>> MiscStage                         0         0              0
>> FlushSorter                       0         0              0
>> InternalResponseStage             0         0              4
>> HintedHandoff                     0         0              0
>> 
>> The other 2 that see minimal cpu usage:
>> 
>> 2 $ ./nodetool -h localhost tpstats
>> Pool Name                    Active   Pending      Completed
>> ReadStage                         0         0              0
>> RequestResponseStage              0         0        9213999
>> MutationStage                     0         0       33233114
>> ReadRepairStage                   0         0              0
>> ReplicateOnWriteStage             0         0              0
>> GossipStage                       0         0         336016
>> AntiEntropyStage                  0         0              0
>> MigrationStage                    0         0              4
>> MemtablePostFlusher               0         0             77
>> StreamStage                       0         0              0
>> FlushWriter                       0         0             77
>> FILEUTILS-DELETE-POOL             0         0             40
>> MiscStage                         0         0              0
>> FlushSorter                       0         0              0
>> InternalResponseStage             0         0              4
>> HintedHandoff                     0         0              0
>> 
>> 
>> 1 $ ./nodetool -h localhost tpstats
>> Pool Name                    Active   Pending      Completed
>> ReadStage                         0         0              0
>> RequestResponseStage              0         0       13796875
>> MutationStage                     0         0       36116662
>> ReadRepairStage                   0         0              0
>> ReplicateOnWriteStage             0         0              0
>> GossipStage                       0         0         336496
>> AntiEntropyStage                  0         0              0
>> MigrationStage                    0         0              4
>> MemtablePostFlusher               0         0             91
>> StreamStage                       0         0              0
>> FlushWriter                       0         0             91
>> FILEUTILS-DELETE-POOL             0         0             43
>> MiscStage                         0         0              0
>> FlushSorter                       0         0              0
>> InternalResponseStage             0         0              4
>> HintedHandoff                     0         0              0


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