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From Jayadev Jayaraman <jdisal...@gmail.com>
Subject Re: What is the ideal value for sstable_size_in_mb when using LeveledCompactionStrategy ?
Date Wed, 18 Sep 2013 19:30:55 GMT
Thanks for the quick reply. We've already upped the ulimit as high as our
Linux distro allows us to ( around 1.8 million  ).

I have a follow-up question. I see that the size of individual nodes in
your use case is quite massive. Does the safe number vary widely based on
differences in underlying hardware, or would you say from experience that
something around 50M for medium to large datasets ( with upped
file-descriptor limits ) is safe for most medium-sized (1 - 5 TB per node)
to high-end (hundreds of TB) hardware ?


On Wed, Sep 18, 2013 at 3:15 PM, Hiller, Dean <Dean.Hiller@nrel.gov> wrote:

>  1.  Always in cassandra up your file descriptor limits on linux and even
> in 0.7 that was the recommendation so cassandra could open tons of files
>  2.  We use 50M for our LCS with no performance issues.  We had it 10M on
> our previous with no issues but a huge amount of files of course with our
> 300T per node.
>
> Dean
>
> From: Jayadev Jayaraman <jdisalive@gmail.com<mailto:jdisalive@gmail.com>>
> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Date: Wednesday, September 18, 2013 1:02 PM
> To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Subject: What is the ideal value for sstable_size_in_mb when using
> LeveledCompactionStrategy ?
>
> We have set up a 24 node (m1.xlarge nodes, 1.7 TB per node) cassandra
> cluster on Amazon EC2 :
>
> version=1.2.9
> replication factor = 2
> snitch=EC2Snitch
> placement_strategy=NetworkTopologyStrategy (with 12 nodes each in 2
> availability zones)
>
> Background on our use-case :
>
> We plan on using hadoop with sstableloader to load 10GB+ of analytics data
> per day ( 100 million+ row keys, 5 or so columns per day on average.) . We
> have chosen LeveledCompactionStrategy in the hope that it constrains the
> number of SSTables that are read in order to retrieve a sliced-predicate
> for a row. We don't want too many file-sockets ( > 1000) open to SSTables
> by the Cassandra JVM as this has caused us network / unreachability issues
> before. We faced this when we were on cassandra 0.8.9 and we were using
> SizeTieredCompactionStrategy and in order to mitigate this, we ran minor
> compaction daily and major compaction semi-regularly to ensure as few
> SSTable files as possible on disk.
>
>
>
>
>
> If we use LeveledCompactionStrategy with a small value for
> sstable_size_in_mb ( default = 5 MB ) , wouldn't that result in a very
> large number of SSTable files on disk ? How does that affect the number of
> file-sockets open (reading the docs, I get the impression that the number
> of SSTable seeks per query is reduced by a large margin) ? But if we use a
> larger value for sstable_size_in_mb, say around 200 MB, there will be 800
> MB of small uncompacted SSTables on disk per column-family to which there
> will inevitably be file-sockets open.
>
> All in all, can someone help us figure out what we should set the value of
> sstable_size_in_mb to ? I figure it's not a very good idea to set it to a
> larger value but I don't know how things perform if we set it to a small
> value. Do we have to run major compaction regularly in this case too ?
>
> Thanks
> Jayadev
>
>
>

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