On Wed, Jul 13, 2011 at 1:00 AM, David Hawthorne <dha...@gmx.3crowd.com> wrote: > Thanks for looking at that. > > Our use case involves supercolumns that have 2-20,000 counters within them. > For a set of continuous updates to one supercolumn, the behavior you're > describing is:
Here's your problem. Don't do that. It's not a counter issue, it's a superColumn limitation. You should only use super columns when you put a small number of subcolumns into it (how many depends on the actual size of the columns, but if we take the example of counters, I'd say that if you have supercolumns with more than 100 counters, you should probably change your model to use composite columns instead of super columns). -- Sylvain > > insert first counter into supercolumn > insert second counter into supercolumn > read entire supercolumn (now 2 wide) > insert third counter into supercolumn > read entire supercolumn (now 3 wide) > insert fourth counter into supercolumn > read entire supercolumn (now 4 wide) > ... > insert 20,000th counter into supercolumn > read entire supercolumn for the 20,000th time (now 20,000 columns wide) > > What happens if I turn replicate on write off and go to RF=3 on a multi-node > cluster? > > Unfortunately, I don't see a way to get the size of the largest supercolumn > in the same way you can get the size of the largest row, so I don't know what > our max number of columns in any supercolumn is. > > The test I was running against the single-node cluster just died, here's a > graph. It held steady at 2.5-3k inserts/sec for a while, and then cassandra > became unresponsive to JMX requests for a while (that's the sharp dip to 0 at > 15:48), after which you can see the ReplicateOnWrite Pending Tasks creep > upwards of 1M when the max row size and max size of any CF on disk both > spike. You can also see the total number of reads done increase sharply at > the same time. All stats are absolute values with the exception of the > inserts/sec, which was multiplied by 10 so it would show up with everything > else. Inserts/sec are from the client's perspective, not from cassandra's. > I can also tell you that the client is seeing a lot of hector timeout > exceptions and retry burden has been pushed back to client. > > > > > > > > On Jul 12, 2011, at 3:26 PM, Sylvain Lebresne wrote: > >> On Wed, Jul 13, 2011 at 12:18 AM, David Hawthorne <dha...@gmx.3crowd.com> >> wrote: >>> >>> On Jul 12, 2011, at 3:02 PM, Sylvain Lebresne wrote: >>> >>>> On Tue, Jul 12, 2011 at 11:42 PM, David Hawthorne <dha...@gmx.3crowd.com> >>>> wrote: >>>>> Well, I was using a large number of clients: I tried configuring a >>>>> hector pool of 20-200 to see what affect that had on throughput. There's >>>>> definitely a point after which there's no gain, so I dialed it back down. >>>>> To clarify a few other things, when I say inserts I mean increments, as >>>>> this test only involves counters. When I say a row is full, I mean I've >>>>> written all of the data into it that belongs in it from our application's >>>>> perspective. Not all rows are the same length, and the average number of >>>>> subcolumns per supercolumn is higher for some rows than for others. >>>>> >>>> >>>> Oh yes, you're using supercolumns. That could help magnify the problem >>>> a little bit, given that to read any subcolumn of a supercolumn, we >>>> have to read the whole supercolumn. Depends how many counters per >>>> supercolumns we're talking about. >>> >>> Does this imply that incrementing 50 counters in one supercolumn in one row >>> in one CF requires 50! reads of the supercolumn? One read of the entire >>> supercolumn for each insert? >> >> Every increment of one of the 50 counters means reading the whole >> superColumn, i.e, 50 counters. That is, there is not more reads, but >> the reads themselves have to read more and so can take longer. >> >>> >>> >>>> >>>>> I'm curious, is it necessary for a read to happen for replication when >>>>> using RF=1? >>>> >>>> No, it's not necessary with RF=1 ... but we still do it :(. Ok, it's >>>> basically a bug, we'll >>>> fix that for 0.8.2. >>>> >>>>> I am currently running a test against a single node cluster, RF=1, >>>>> CL.ONE, 4 connections/concurrent increments, and graphing various data >>>>> points. If something interesting happens, I'll send a graph. >>>>> >>>>> When you say stagger writes, do you mean just lower the overall number of >>>>> increments/sec my client is attempting, >>>> >>>> Yes, this is what I mean. >>>> >>>>> or do you mean I should stagger the load amongst many CFs/rows at once? >>>>> Right now I'm writing heavily into a small set of rows, each going into 3 >>>>> CFs, before moving on to the next small set of rows. >>>>> >>>>> >>>>> On Jul 12, 2011, at 12:26 PM, Sylvain Lebresne wrote: >>>>> >>>>>> When you do counter increment at CL.ONE, the write is acknowledged as >>>>>> soon as the first replica getting the the write has pushed the >>>>>> increment into his memtable. However, there is a read happening for >>>>>> the replication to the other replicas (this is necessary to the >>>>>> counter design). What is happening is that our nodes are not able to >>>>>> do those reads fast enough. Or, another way to see it is that you are >>>>>> writing faster than you cluster can handle. >>>>>> >>>>>> I've opened https://issues.apache.org/jira/browse/CASSANDRA-2889 to do >>>>>> something about that, but for now you'll have to stagger your writes. >>>>>> I'm more surprised that tasks on the replicate on write stage would >>>>>> stack up at QUORUM, unless you're using a very large number of >>>>>> clients. >>>>>> >>>>>> -- >>>>>> Sylvain >>>>>> >>>>>> On Tue, Jul 12, 2011 at 8:57 AM, David Hawthorne <dha...@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 >>>>> >>>>> >>> >>> > > >
