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From Benjamin Black...@b3k.us>
Subject Re: Problem with Deletes
Date Sun, 20 Jun 2010 08:48:56 GMT
http://wiki.apache.org/cassandra/DistributedDeletes

On Thu, Jun 17, 2010 at 9:10 AM, Amir <amir74tt@yahoo.com> wrote:
> Hi All,
>
> I'm running a benchmark on Cassandra while using a benchmark client which I've
> written myself.
>
> I'm running the following scenario:
> One Cassandra node on the same machine as the client.
> The client writes a new key every 1 second and deletes it after 10 seconds, so
> at any given time there should be only 10 keys.
> The key value size is 2K.
>
> When I ran this scenario I looked at the data folder and saw that initially
> cassandra created 4 files (SSTables) of ~130K and then compacted them to 20K
> (which is exactly what I expected 10 keys * 2K = 20K).
> And afterwards there where another 3 130K files which were compacted together
> with the first 20K file to a new 20K file, and so on...
>
> This scenario ran exactly as I excepted.
>
> Now I ran the same scenario but this time with key value size=2M.
>
> When I ran this scenario initially cassandra created 4 files (SSTables) of ~64M
> and then compacted them to 20M (which is exactly what I expected 10 keys * 2M =
> 20M). But after creating another 3 64M files - the problem started!
> It didn't compact them with the first 20M - instead it created another 64M file
> and compacted all 4 of them to 260M file (!), and after creating another 4 64M
> files it compacted them to another 260M file and so on...
>
> It looks to me like in this scenario for some reason the compaction doesn't
> make any deletes. I don't have any idea why :-(
>
> Additional info which I should mention:
> In the storage-conf.xml the following are not default:
> GCGraceSeconds = 0
> MemtableFlushAfterMinutes = 1
> <ColumnFamily Name="Standard2"
>                    CompareWith="UTF8Type"
>                    KeysCached="99%"/>
>
>
> Thanks a lot for your help,
>
> Amir
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