"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 Beware of the major compaction on SizeTiered, it will create 2 giant SSTables and the expired/outdated/tombstone columns in this big file will be never cleaned since the SSTable will never get a chance to be compacted again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 >
