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From Jonathan Lasko <>
Subject Re: Profile a (batch) scan
Date Fri, 26 Aug 2016 22:31:08 GMT
I haven't had time to dig into it yet but am hoping the Zipkin will help 
with some of these insights. (Unless that is the distributed trace you 
were referring to?)


On 08/26/2016 04:54 PM, Mario Pastorelli wrote:
> I would like to understand the performance of a batch scan and I would 
> like to have some hints on how to proceed. I have enabled the 
> distributed trace, and it tells me that some batch scanner threads 
> take much more time than others to complete but this is not helpful 
> enough because it's not telling me why some threads take more. My gut 
> feeling is that one batch thread is scanning more data than the 
> others, which means that the data is not well distributed for a query, 
> but I use a random shard byte as prefix of the keys which should 
> guarantee that data of the same range is almost equally distributed 
> among the tservers. I enabled JMX on the tservers and attached 
> jvisualvm to get an idea of the state of each tserver but I couldn't 
> find anything meaningful. I would like to know if there is a way to 
> profile what's going on on a single tserver for a single scan thread 
> and by this I mean:
>  1. where are the tablets required by a scan? Which tablet server?
>  2. how fast was the lookups on the index for that scan?
>  3. how many bytes/records were read for that scan without the iterators
>  4. how many seeks are done by the scan and possibly why
> The main Accumulo UI is fine to get an overview of Accumulo but don't 
> really give you any information about the performance of a single 
> query and it seems to me that they are heavily affected by what 
> iterators do. Profiling a single scan is much more interesting. Is 
> there a way to profile a single (batch) scan in Accumulo such that I 
> have a complete overview of the entire process of reading and sending 
> back records to the driver?
> Thanks,
> Mario
> -- 
> Mario Pastorelli| TERALYTICS
> *software engineer*
> Teralytics AG | Zollstrasse 62 | 8005 Zurich | Switzerland
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