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
> +55 48 3232.3200
