Thats great Will, if you could update the thread with the actions you decide to take and the results that would be great.
Mark On Fri, Apr 11, 2014 at 5:53 PM, William Oberman <ober...@civicscience.com>wrote: > I've learned a *lot* from this thread. My thanks to all of the > contributors! > > Paulo: Good luck with LCS. I wish I could help there, but all of my CF's > are SizeTiered (mostly as I'm on the same schema/same settings since 0.7...) > > will > > > > On Fri, Apr 11, 2014 at 12:14 PM, Mina Naguib <mina.nag...@adgear.com>wrote: > >> >> Levelled Compaction is a wholly different beast when it comes to >> tombstones. >> >> The tombstones are inserted, like any other write really, at the lower >> levels in the leveldb hierarchy. >> >> They are only removed after they have had the chance to "naturally" >> migrate upwards in the leveldb hierarchy to the highest level in your data >> store. How long that takes depends on: >> 1. The amount of data in your store and the number of levels your LCS >> strategy has >> 2. The amount of new writes entering the bottom funnel of your leveldb, >> forcing upwards compaction and combining >> >> To give you an idea, I had a similar scenario and ran a (slow, throttled) >> delete job on my cluster around December-January. Here's a graph of the >> disk space usage on one node. Notice the still-diclining usage long after >> the cleanup job has finished (sometime in January). I tend to think of >> tombstones in LCS as little bombs that get to explode much later in time: >> >> http://mina.naguib.ca/images/tombstones-cassandra-LCS.jpg >> >> >> >> On 2014-04-11, at 11:20 AM, Paulo Ricardo Motta Gomes < >> paulo.mo...@chaordicsystems.com> wrote: >> >> I have a similar problem here, I deleted about 30% of a very large CF >> using LCS (about 80GB per node), but still my data hasn't shrinked, even if >> I used 1 day for gc_grace_seconds. Would nodetool scrub help? Does nodetool >> scrub forces a minor compaction? >> >> Cheers, >> >> Paulo >> >> >> On Fri, Apr 11, 2014 at 12:12 PM, Mark Reddy <mark.re...@boxever.com>wrote: >> >>> Yes, running nodetool compact (major compaction) creates one large >>> SSTable. This will mess up the heuristics of the SizeTiered strategy (is >>> this the compaction strategy you are using?) leading to multiple 'small' >>> SSTables alongside the single large SSTable, which results in increased >>> read latency. You will incur the operational overhead of having to manage >>> compactions if you wish to compact these smaller SSTables. For all these >>> reasons it is generally advised to stay away from running compactions >>> manually. >>> >>> Assuming that this is a production environment and you want to keep >>> everything running as smoothly as possible I would reduce the gc_grace on >>> the CF, allow automatic minor compactions to kick in and then increase the >>> gc_grace once again after the tombstones have been removed. >>> >>> >>> On Fri, Apr 11, 2014 at 3:44 PM, William Oberman < >>> ober...@civicscience.com> wrote: >>> >>>> So, if I was impatient and just "wanted to make this happen now", I >>>> could: >>>> >>>> 1.) Change GCGraceSeconds of the CF to 0 >>>> 2.) run nodetool compact (*) >>>> 3.) Change GCGraceSeconds of the CF back to 10 days >>>> >>>> Since I have ~900M tombstones, even if I miss a few due to impatience, >>>> I don't care *that* much as I could re-run my clean up tool against the now >>>> much smaller CF. >>>> >>>> (*) A long long time ago I seem to recall reading advice about "don't >>>> ever run nodetool compact", but I can't remember why. Is there any bad >>>> long term consequence? Short term there are several: >>>> -a heavy operation >>>> -temporary 2x disk space >>>> -one big SSTable afterwards >>>> But moving forward, everything is ok right? >>>> CommitLog/MemTable->SStables, minor compactions that merge SSTables, >>>> etc... The only flaw I can think of is it will take forever until the >>>> SSTable minor compactions build up enough to consider including the big >>>> SSTable in a compaction, making it likely I'll have to self manage >>>> compactions. >>>> >>>> >>>> >>>> On Fri, Apr 11, 2014 at 10:31 AM, Mark Reddy <mark.re...@boxever.com>wrote: >>>> >>>>> Correct, a tombstone will only be removed after gc_grace period has >>>>> elapsed. The default value is set to 10 days which allows a great deal of >>>>> time for consistency to be achieved prior to deletion. If you are >>>>> operationally confident that you can achieve consistency via anti-entropy >>>>> repairs within a shorter period you can always reduce that 10 day >>>>> interval. >>>>> >>>>> >>>>> Mark >>>>> >>>>> >>>>> On Fri, Apr 11, 2014 at 3:16 PM, William Oberman < >>>>> ober...@civicscience.com> wrote: >>>>> >>>>>> I'm seeing a lot of articles about a dependency between removing >>>>>> tombstones and GCGraceSeconds, which might be my problem (I just checked, >>>>>> and this CF has GCGraceSeconds of 10 days). >>>>>> >>>>>> >>>>>> On Fri, Apr 11, 2014 at 10:10 AM, tommaso barbugli < >>>>>> tbarbu...@gmail.com> wrote: >>>>>> >>>>>>> compaction should take care of it; for me it never worked so I run >>>>>>> nodetool compaction on every node; that does it. >>>>>>> >>>>>>> >>>>>>> 2014-04-11 16:05 GMT+02:00 William Oberman <ober...@civicscience.com >>>>>>> >: >>>>>>> >>>>>>> I'm wondering what will clear tombstoned rows? nodetool cleanup, >>>>>>>> nodetool repair, or time (as in just wait)? >>>>>>>> >>>>>>>> I had a CF that was more or less storing session information. >>>>>>>> After some time, we decided that one piece of this information was >>>>>>>> pointless to track (and was 90%+ of the columns, and in 99% of those >>>>>>>> cases >>>>>>>> was ALL columns for a row). I wrote a process to remove all of those >>>>>>>> columns (which again in a vast majority of cases had the effect of >>>>>>>> removing >>>>>>>> the whole row). >>>>>>>> >>>>>>>> This CF had ~1 billion rows, so I expect to be left with ~100m >>>>>>>> rows. After I did this mass delete, everything was the same size on >>>>>>>> disk >>>>>>>> (which I expected, knowing how tombstoning works). It wasn't 100% >>>>>>>> clear to >>>>>>>> me what to poke to cause compactions to clear the tombstones. First I >>>>>>>> tried nodetool cleanup on a candidate node. But, afterwards the disk >>>>>>>> usage >>>>>>>> was the same. Then I tried nodetool repair on that same node. But >>>>>>>> again, >>>>>>>> disk usage is still the same. The CF has no snapshots. >>>>>>>> >>>>>>>> So, am I misunderstanding something? Is there another operation to >>>>>>>> try? Do I have to "just wait"? I've only done cleanup/repair on one >>>>>>>> node. >>>>>>>> Do I have to run one or the other over all nodes to clear tombstones? >>>>>>>> >>>>>>>> Cassandra 1.2.15 if it matters, >>>>>>>> >>>>>>>> Thanks! >>>>>>>> >>>>>>>> will >>>>>>>> >>>>>>> >>>>>>> >>>>>> >>>>>> >>>>>> >>>>> >>>> >>> >> >> >> -- >> *Paulo Motta* >> >> Chaordic | *Platform* >> *www.chaordic.com.br <http://www.chaordic.com.br/>* >> +55 48 3232.3200 >> >> >> > > >
