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From Batranut Bogdan <batra...@yahoo.com>
Subject Re: Cassandra slow on some reads
Date Sat, 15 Mar 2014 20:48:38 GMT
Hello,

Yes for the first query the server can be slow but no matter what is should not take 10 seconds
to get one key from a column family. I can see this happening if I have times like 20 ms for
some queries and let's say 300 ms for uncached ones. But I have responses that take from 8
to 20 ms (420 out of 450 queries) and 30 response that take from 5 to 13 seconds. It is this
HUGE difference that bothers me.



On Friday, March 14, 2014 9:18 PM, Manoj Khangaonkar <khangaonkar@gmail.com> wrote:
 

>
>
>
>I have ~450 queries that are like this: SELECT * FROM table where key = 'some string'
and ts = some value; some value is close to present time.
>
>
>The problem:
>
>
>About 10 - 20 % of these queries take more than 5 seconds to execute, in fact, the majority
of those take around 10 seconds.
>When investigating I saw that if I have a slow response and I redo the query it will finish
in 8 - 10 MILIseconds like the rest of the queries that I have. 
>
>
>

Most likely for the first slow query, the server has to go looking in SSTables on disk. 2nd
fast response is returned from memory. I am not sure how much data each node is managing.
But try adding more nodes , so that each node is managing fewer keys. More nodes with recommended
heap size of 8G is better than fewer nodes with bigger heap size.


regards


-- 
http://khangaonkar.blogspot.com/
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