If the issue is related to I/O, you're going to want to determine if you're saturated. Take a look at `iostat -dmx 1`, you'll see avgqu-sz (queue size) and svctm, (service time). The higher those numbers are, the most overwhelmed your disk is.
On Sun, Oct 26, 2014 at 12:01 PM, DuyHai Doan <doanduy...@gmail.com> wrote: > Hello Maxime > > Increasing the flush writers won't help if your disk I/O is not keeping up. > > I've had a look into the log file, below are some remarks: > > 1) There are a lot of SSTables on disk for some tables (events for example, > but not only). I've seen that some compactions are taking up to 32 SSTables > (which corresponds to the default max value for SizeTiered compaction). > > 2) There is a secondary index that I found suspicious : loc.loc_id_idx. As > its name implies I have the impression that it's an index on the id of the > loc which would lead to almost an 1-1 relationship between the indexed value > and the original loc. Such index should be avoided because they do not > perform well. If it's not an index on the loc_id, please disregard my remark > > 3) There is a clear imbalance of SSTable count on some nodes. In the log, I > saw: > > INFO [STREAM-IN-/xxxx.xxxx.xxxx.20] 2014-10-25 02:21:43,360 > StreamResultFuture.java:166 - [Stream #a6e54ea0-5bed-11e4-8df5-f357715e1a79 > ID#0] Prepare completed. Receiving 163 files(4 111 187 195 bytes), sending 0 > files(0 bytes) > > INFO [STREAM-IN-/xxxx.xxxx.xxxx.81] 2014-10-25 02:21:46,121 > StreamResultFuture.java:166 - [Stream #a6e54ea0-5bed-11e4-8df5-f357715e1a79 > ID#0] Prepare completed. Receiving 154 files(3 332 779 920 bytes), sending 0 > files(0 bytes) > > INFO [STREAM-IN-/xxxx.xxxx.xxxx.71] 2014-10-25 02:21:50,494 > StreamResultFuture.java:166 - [Stream #a6e54ea0-5bed-11e4-8df5-f357715e1a79 > ID#0] Prepare completed. Receiving 1315 files(4 606 316 933 bytes), sending > 0 files(0 bytes) > > INFO [STREAM-IN-/xxxx.xxxx.xxxx.217] 2014-10-25 02:21:51,036 > StreamResultFuture.java:166 - [Stream #a6e54ea0-5bed-11e4-8df5-f357715e1a79 > ID#0] Prepare completed. Receiving 1640 files(3 208 023 573 bytes), sending > 0 files(0 bytes) > > As you can see, the existing 4 nodes are streaming data to the new node and > on average the data set size is about 3.3 - 4.5 Gb. However the number of > SSTables is around 150 files for nodes xxxx.xxxx.xxxx.20 and > xxxx.xxxx.xxxx.81 but goes through the roof to reach 1315 files for > xxxx.xxxx.xxxx.71 and 1640 files for xxxx.xxxx.xxxx.217 > > The total data set size is roughly the same but the file number is x10, > which mean that you'll have a bunch of tiny files. > > I guess that upon reception of those files, there will be a massive flush > to disk, explaining the behaviour you're facing (flush storm) > > I would suggest looking on nodes xxxx.xxxx.xxxx.71 and xxxx.xxxx.xxxx.217 to > check for the total SSTable count for each table to confirm this intuition > > Regards > > > On Sun, Oct 26, 2014 at 4:58 PM, Maxime <maxim...@gmail.com> wrote: >> >> I've emailed you a raw log file of an instance of this happening. >> >> I've been monitoring more closely the timing of events in tpstats and the >> logs and I believe this is what is happening: >> >> - For some reason, C* decides to provoke a flush storm (I say some reason, >> I'm sure there is one but I have had difficulty determining the behaviour >> changes between 1.* and more recent releases). >> - So we see ~ 3000 flush being enqueued. >> - This happens so suddenly that even boosting the number of flush writers >> to 20 does not suffice. I don't even see "all time blocked" numbers for it >> before C* stops responding. I suspect this is due to the sudden OOM and GC >> occurring. >> - The last tpstat that comes back before the node goes down indicates 20 >> active and 3000 pending and the rest 0. It's by far the anomalous activity. >> >> Is there a way to throttle down this generation of Flush? C* complains if >> I set the queue_size to any value (deprecated now?) and boosting the threads >> does not seem to help since even at 20 we're an order of magnitude off. >> >> Suggestions? Comments? >> >> >> On Sun, Oct 26, 2014 at 2:26 AM, DuyHai Doan <doanduy...@gmail.com> wrote: >>> >>> Hello Maxime >>> >>> Can you put the complete logs and config somewhere ? It would be >>> interesting to know what is the cause of the OOM. >>> >>> On Sun, Oct 26, 2014 at 3:15 AM, Maxime <maxim...@gmail.com> wrote: >>>> >>>> Thanks a lot that is comforting. We are also small at the moment so I >>>> definitely can relate with the idea of keeping small and simple at a level >>>> where it just works. >>>> >>>> I see the new Apache version has a lot of fixes so I will try to upgrade >>>> before I look into downgrading. >>>> >>>> >>>> On Saturday, October 25, 2014, Laing, Michael >>>> <michael.la...@nytimes.com> wrote: >>>>> >>>>> Since no one else has stepped in... >>>>> >>>>> We have run clusters with ridiculously small nodes - I have a >>>>> production cluster in AWS with 4GB nodes each with 1 CPU and disk-based >>>>> instance storage. It works fine but you can see those little puppies >>>>> struggle... >>>>> >>>>> And I ran into problems such as you observe... >>>>> >>>>> Upgrading Java to the latest 1.7 and - most importantly - reverting to >>>>> the default configuration, esp. for heap, seemed to settle things down >>>>> completely. Also make sure that you are using the 'recommended production >>>>> settings' from the docs on your boxen. >>>>> >>>>> However we are running 2.0.x not 2.1.0 so YMMV. >>>>> >>>>> And we are switching to 15GB nodes w 2 heftier CPUs each and SSD >>>>> storage - still a 'small' machine, but much more reasonable for C*. >>>>> >>>>> However I can't say I am an expert, since I deliberately keep things so >>>>> simple that we do not encounter problems - it just works so I dig into >>>>> other >>>>> stuff. >>>>> >>>>> ml >>>>> >>>>> >>>>> On Sat, Oct 25, 2014 at 5:22 PM, Maxime <maxim...@gmail.com> wrote: >>>>>> >>>>>> Hello, I've been trying to add a new node to my cluster ( 4 nodes ) >>>>>> for a few days now. >>>>>> >>>>>> I started by adding a node similar to my current configuration, 4 GB >>>>>> or RAM + 2 Cores on DigitalOcean. However every time, I would end up >>>>>> getting >>>>>> OOM errors after many log entries of the type: >>>>>> >>>>>> INFO [SlabPoolCleaner] 2014-10-25 13:44:57,240 >>>>>> ColumnFamilyStore.java:856 - Enqueuing flush of mycf: 5383 (0%) on-heap, >>>>>> 0 >>>>>> (0%) off-heap >>>>>> >>>>>> leading to: >>>>>> >>>>>> ka-120-Data.db (39291 bytes) for commitlog position >>>>>> ReplayPosition(segmentId=1414243978538, position=23699418) >>>>>> WARN [SharedPool-Worker-13] 2014-10-25 13:48:18,032 >>>>>> AbstractTracingAwareExecutorService.java:167 - Uncaught exception on >>>>>> thread >>>>>> Thread[SharedPool-Worker-13,5,main]: {} >>>>>> java.lang.OutOfMemoryError: Java heap space >>>>>> >>>>>> Thinking it had to do with either compaction somehow or streaming, 2 >>>>>> activities I've had tremendous issues with in the past; I tried to slow >>>>>> down >>>>>> the setstreamthroughput to extremely low values all the way to 5. I also >>>>>> tried setting setcompactionthoughput to 0, and then reading that in some >>>>>> cases it might be too fast, down to 8. Nothing worked, it merely vaguely >>>>>> changed the mean time to OOM but not in a way indicating either was >>>>>> anywhere >>>>>> a solution. >>>>>> >>>>>> The nodes were configured with 2 GB of Heap initially, I tried to >>>>>> crank it up to 3 GB, stressing the host memory to its limit. >>>>>> >>>>>> After doing some exploration (I am considering writing a Cassandra Ops >>>>>> documentation with lessons learned since there seems to be little of it >>>>>> in >>>>>> organized fashions), I read that some people had strange issues on >>>>>> lower-end >>>>>> boxes like that, so I bit the bullet and upgraded my new node to a 8GB + >>>>>> 4 >>>>>> Core instance, which was anecdotally better. >>>>>> >>>>>> To my complete shock, exact same issues are present, even raising the >>>>>> Heap memory to 6 GB. I figure it can't be a "normal" situation anymore, >>>>>> but >>>>>> must be a bug somehow. >>>>>> >>>>>> My cluster is 4 nodes, RF of 2, about 160 GB of data across all nodes. >>>>>> About 10 CF of varying sizes. Runtime writes are between 300 to 900 / >>>>>> second. Cassandra 2.1.0, nothing too wild. >>>>>> >>>>>> Has anyone encountered these kinds of issues before? I would really >>>>>> enjoy hearing about the experiences of people trying to run small-sized >>>>>> clusters like mine. From everything I read, Cassandra operations go very >>>>>> well on large (16 GB + 8 Cores) machines, but I'm sad to report I've had >>>>>> nothing but trouble trying to run on smaller machines, perhaps I can >>>>>> learn >>>>>> from other's experience? >>>>>> >>>>>> Full logs can be provided to anyone interested. >>>>>> >>>>>> Cheers >>>>> >>>>> >>> >> > -- Jon Haddad http://www.rustyrazorblade.com twitter: rustyrazorblade