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From aaron morton <aa...@thelastpickle.com>
Subject Re: High-read latency for non-existing rows with LCS and 1.2.5
Date Sat, 29 Jun 2013 05:01:55 GMT
> We are using Leveled Compaction with Cassandra 1.2.5. Our sstable size is 100M. On each
node,
> we have anywhere from 700+ to 800+ sstables (for all levels). The bloom_filter_fp_chance
is set at 0.000744.
The current default bloom_filter_fp_chance is 0.1 for levelled compaction. Reducing this (and
running nodetool upgradesstables) will reduce the bloom filter size significantly. 

>  the latency is running into hundreds of milliseconds and sometimes seconds.
Check the number of SSTables per read using nodetool cfhistograms. With levelled compaction
you should not see above 3 http://www.datastax.com/dev/blog/when-to-use-leveled-compaction

Cheers

 
-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 28/06/2013, at 7:44 AM, sankalp kohli <kohlisankalp@gmail.com> wrote:

> Try doing request tracing. 
> http://www.datastax.com/dev/blog/tracing-in-cassandra-1-2
> 
> 
> On Thu, Jun 27, 2013 at 2:40 PM, Bao Le <lvqb@yahoo.com> wrote:
> Hi,
> 
>     We are using Leveled Compaction with Cassandra 1.2.5. Our sstable size is 100M. On
each node,
> we have anywhere from 700+ to 800+ sstables (for all levels). The bloom_filter_fp_chance
is set at 0.000744.
> 
>   For read requests that ask for existing row records, the latency is great, mostly under
20 milliseconds with key cache and row cache set. For read requests that ask for non-existing
row records (not because of deletes, but rather, have never been in the system to start with),
the latency is running into hundreds of milliseconds and sometimes seconds.
> 
>   Just wonder if anyone has come across this before and has some pointers on how to reduce
the latency in this case.
> 
> Thanks
> Bao
> 
> 
> 
> 


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