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From Batranut Bogdan <batra...@yahoo.com>
Subject Re: Cassandra slow on some reads
Date Sat, 15 Mar 2014 22:53:15 GMT
Whooops 

On one of the nodes when running my tests I found an exception

java FileNotFoundException : file .... xxxx-Data.db not found
at org.apache.cassandra.io.compress.CompressedThrottledReader.open(CompressedThrottledReader.java:52


also got another one coming from
java.io.RandomAccessFile.open(native method)
java.io.RandomAccessFile..<init> (RandomAccesFile.java:241)
org.apache.cassandra.io.util.RandomAccessReader.<init>(RandomAccessReader.java:58)



On Saturday, March 15, 2014 10:52 PM, Benedict Elliott Smith <belliottsmith@datastax.com>
wrote:
 
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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