Re: Latency variation, average latency continued

[Dan Di Spaltro <da...@gmail.com>]

Moving over to the right mailing list.


On Sun, Mar 30, 2014 at 2:26 PM, WeiZheng Zhou <zh...@gmail.com>wrote:

> Hi,
>
> We are doing some experiments requiring us to measure the latency
> correctly. However, the latency varies a lot from run to run. As shown in
> the below figure, we generated five tables, namely table 1 to table 5.
> These tables have exactly the same schema, i.e. the same number of rows,
> the same number of columns etc. Then we run the following code on these
> tables:
>
> for each run from 1:10
>      for each table 1:5
>           connect to phoenix
>           select * from table where value > *9000*   //max value =10,000,
> therefore select 10% of total rows
>           measure the latency
>           close connection
>      endfor
> endfor
>
> for each run from 1:10
>      for each table 1:5
>           connect to phoenix
>           select * from table where value > *5000*   //max value =10,000,
> therefore select 50% of total rows
>           measure the latency
>           close connection
>      endfor
> endfor
>
> Since, these tables have the same schema and we run the same queries. We
> should expect the same latency.
>
> In the first figure, we select value > 9000.  As we can see, the latency
> on each tables agrees well after the second run. However, at the first run,
> the latency of table 1 is much longer than other tables. So, what makes the
> table 1 differ from other tables, considering they have the same contents
> and run the same query ?
>
> In the second figure, we select value > 5000
> Maybe because of cache, the latency of table 1 is decreased after the
> first run. However, for other tables,  the latencies are increasing, not by
> a small amount by almost doubled. Do you have any idea about this large
> increasing ?
>
> So, my question is, what are the possible features of phoenix, hbase  can
> explain this increasing and decreasing trend of latency ?
>
> Thanks a lot
>
> Weizheng Zhou
>
>
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-- 
Dan Di Spaltro