"Tombstones will be a very important issue for me since the dataset is very much a rolling dataset using TTLs heavily."
--> You can try the new DateTiered compaction strategy ( https://issues.apache.org/jira/browse/CASSANDRA-6602) released on 2.1.1 if you have a time series data model to eliminate tombstones On Mon, Oct 27, 2014 at 5:47 PM, Laing, Michael <michael.la...@nytimes.com> wrote: > Again, from our experience w 2.0.x: > > Revert to the defaults - you are manually setting heap way too high IMHO. > > On our small nodes we tried LCS - way too much compaction - switch all CFs > to STCS. > > We do a major rolling compaction on our small nodes weekly during less > busy hours - works great. Be sure you have enough disk. > > We never explicitly delete and only use ttls or truncation. You can set GC > to 0 in that case, so tombstones are more readily expunged. There are a > couple threads in the list that discuss this... also normal rolling repair > becomes optional, reducing load (still repair if something unusual happens > tho...). > > In your current situation, you need to kickstart compaction - are there > any CFs you can truncate at least temporarily? Then try compacting a small > CF, then another, etc. > > Hopefully you can get enough headroom to add a node. > > ml > > > > > On Sun, Oct 26, 2014 at 6:24 PM, Maxime <maxim...@gmail.com> wrote: > >> Hmm, thanks for the reading. >> >> I initially followed some (perhaps too old) maintenance scripts, which >> included weekly 'nodetool compact'. Is there a way for me to undo the >> damage? Tombstones will be a very important issue for me since the dataset >> is very much a rolling dataset using TTLs heavily. >> >> On Sun, Oct 26, 2014 at 6:04 PM, DuyHai Doan <doanduy...@gmail.com> >> wrote: >> >>> "Should doing a major compaction on those nodes lead to a restructuration >>> of the SSTables?" --> Beware of the major compaction on SizeTiered, it will >>> create 2 giant SSTables and the expired/outdated/tombstone columns in this >>> big file will be never cleaned since the SSTable will never get a chance to >>> be compacted again >>> >>> Essentially to reduce the fragmentation of small SSTables you can stay >>> with SizeTiered compaction and play around with compaction properties (the >>> thresholds) to make C* group a bunch of files each time it compacts so that >>> the file number shrinks to a reasonable count >>> >>> Since you're using C* 2.1 and anti-compaction has been introduced, I >>> hesitate advising you to use Leveled compaction as a work-around to reduce >>> SSTable count. >>> >>> Things are a little bit more complicated because of the incremental >>> repair process (I don't know whether you're using incremental repair or not >>> in production). The Dev blog says that Leveled compaction is performed only >>> on repaired SSTables, the un-repaired ones still use SizeTiered, more >>> details here: >>> http://www.datastax.com/dev/blog/anticompaction-in-cassandra-2-1 >>> >>> Regards >>> >>> >>> >>> >>> >>> On Sun, Oct 26, 2014 at 9:44 PM, Jonathan Haddad <j...@jonhaddad.com> >>> wrote: >>> >>>> 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 >>>> >>> >>> >> >
