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From Aaron Morton <aa...@thelastpickle.com>
Subject Re: Cassandra SSTable deletion/load reporting question
Date Mon, 28 Oct 2013 06:47:09 GMT
> 1.2 w/ vnodes using LeveledCompactionStrategy, using 128 mb SSTables.
If you are using LCS the amount of overwritten / deleted data left will be small. 

Your row will be present in only 1 sstable per level. The number of levels is included in
the output from nodetool cfstats on the sstable count line. It shows the number of sstables
at each level. 

If you really want to know which sstables contain your row use either sstable2json or sstablekeys.


Cheers

-----------------
Aaron Morton
New Zealand
@aaronmorton

Co-Founder & Principal Consultant
Apache Cassandra Consulting
http://www.thelastpickle.com

On 26/10/2013, at 9:20 am, Jasdeep Hundal <dsjas297@gmail.com> wrote:

> Thanks Rob.
> 
> Will checkout the tool you linked to. In our case it's definitely not the tombstones
hanging around since we write entire rows at once and the amount of data in a row is far,
far greater than the space a tombstone takes.
> 
> Jasdeep
> 
> 
> On Fri, Oct 25, 2013 at 1:14 PM, Robert Coli <rcoli@eventbrite.com> wrote:
> On Fri, Oct 25, 2013 at 1:10 PM, Jasdeep Hundal <dsjas297@gmail.com> wrote:
> 
> After performing a large set of deletes on our cluster, a few hundred gigabytes work
(essentially cleaning out nearly all old data), we noticed that nodetool reported about the
same load as before.
> 
> Tombstones are purgeable only after gc_grace_seconds has elapsed, and only if all SSTables
which contain fragments of that row are involved in the compaction.
>  
> With my understanding, running a repair should have triggered compactions between SSTable
files and reference counting on the subsequent restart of cassandra on a node should have
cleared the old files, but this did not appear to happen. The load did not start going down
until we were writing to the cluster again.
> 
> Repair is unrelated to minor compaction, except in that it creates new SSTables via streaming,
which may trigger minor compaction.
>  
> I suspect that there are a few values hanging around in the old tables so the references
stayed intact, can anyone confirm this?
> 
> Stop suspecting and measure with checksstablegarbage : https://github.com/cloudian/support-tools
>  
> What's a bit more important for me is being able to accurately report the size of the
"active" data set, since nodetool doesn't seem to be useful for this. I use counters for reporting
some of this, but is there a single source of truth for this, especially since counters do
occasionally miss updates.
> 
> In very new versions of Cassandra, there is tracking of and metrics available for what
percentage of data in a SSTable is expired.
> 
> =Rob
>  
> 


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