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From "Hiller, Dean" <>
Subject Re: Insert v/s Update performance
Date Wed, 27 Mar 2013 00:15:00 GMT
LCS is generally used for high read vs. write ratio though it sounds like you may be doing
a heavy write load instead.  LCS will involve more compactions as you write to the system
compared to STCS because LCS is always trying to keep a 1 to 10 ratio between levels.  While
LCS will involve more compaction in general(more I/o, more cpu), I am not sure on update vs.
insert though From what I understand STCS will happily duplicate rows across SS tables while
LCS does not like to do this so as you update you will constantly compact….well, that is
my understanding.  Have you tried STCS out at all?  (ps. This is just from what I understand
so take with a grain of salt).

Also, there are some great tools in the nodetool tool as well so you can get nodetool compactionstats,
etc. etc. and see how backlogged you are in pending tasks….how many pending?


From: Jay Svc <<>>
Reply-To: "<>" <<>>
Date: Tuesday, March 26, 2013 6:08 PM
To: "<>" <<>>
Subject: Re: Insert v/s Update performance

Thanks Dean,

I have used LCS with sstable_size_in_mb of 15. I have also tried bigger sstable_size_in_mb
and observed simillar behavior.

Does compaction works differently for update v/s Insert? I belive all keys goes to single
SST. What other options I should look into?


On Tue, Mar 26, 2013 at 6:18 PM, Hiller, Dean <<>>
Most likely compaction kicks in as updates cause duplicated rows in STCS and compaction causes
load that may not have been there before(check your logs).  Also, you can increase the number
of nodes in your cluster as well to better handle the load.


From: Jay Svc <<><<>>>
Reply-To: "<><<>>"
Date: Tuesday, March 26, 2013 5:05 PM
To: "<><<>>"
Subject: Insert v/s Update performance

Hi Team,

I have this 3 node cluster. I am writing data to these node at the rate of 2,000 records/second.
What I observed that if I do inserts. (Means records for those keys does not exist, my column
family has 0 records to start with) then I have better write performacne, low SSTable count,
low pending compaction and write latency is acceptable and CPU utilization on each node between
35% to 85%.

When I ran same test but for update this time (means records already exists in Column family
with same key), I observed that my SSTable count gone high 3 times. Pending compactions gone
high more than 2 times and write latency has gone high too and CPU utilization was almost
92% to 100%.

What is a reason of deteriorating Update performance v/s Insert performance. Since this is
critical you help is highly appriciated.

P.S. I also observed that high number of pending Mutation Stage on my nodetool tpstats.


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