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From Benedict Elliott Smith <belliottsm...@datastax.com>
Subject Re: Cassandra slow on some reads
Date Sat, 15 Mar 2014 20:52:05 GMT
Post the server logs and traces of one of the lengthy queries?
On 15 Mar 2014 20:49, "Batranut Bogdan" <batranub@yahoo.com> wrote:

> 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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