Hi, I understood what you wanted to say of using SUM and COUNT for calculating AVERAGE. But as i understand this will work very well with Distributed operations..... what about operations like Median.
Also i wanted to ask how the query will be broken up in the execution engine. I have gone through the Apache drill documentation and also Google Dremel paper, and i am still confused that how multiple level of aggregation will be created inside one tree. Thanks! ________________________________ From: devansh kumar <[email protected]> To: Andrew Brust <[email protected]>; "[email protected]" <[email protected]>; "[email protected]" <[email protected]> Sent: Friday, April 5, 2013 10:18 AM Subject: Re: Basic queries regarding Apache Drill working Hi, As Andrew asked, how will average work without an operation of Reduce present. Can you explain more on how will the data be aggregated? ________________________________ From: Andrew Brust <[email protected]> To: "[email protected]" <[email protected]>; devansh kumar <[email protected]> Sent: Thursday, April 4, 2013 8:00 PM Subject: RE: Basic queries regarding Apache Drill working Still not sure I follow (and pardon what must be a very rudimentary misunderstanding on my part) how you get an average across a data set if the data is split across nodes. With MapReduce, the reducer can get it because all data for a given key is kept to one node. How would this work with Drill? -----Original Message----- From: Ted Dunning [mailto:[email protected]] Sent: Thursday, April 4, 2013 9:27 AM To: [email protected]; devansh kumar Subject: Re: Basic queries regarding Apache Drill working On Thu, Apr 4, 2013 at 12:27 PM, devansh kumar <[email protected]>wrote: > Hi, > > I am new and am trying to understand how Apache Drill works but i > have a few queries. > Can anyone help me understand these things? > > 1. > I am trying to understand if the execution engine is going to break up > the data. > Normally the data will already have been broken up across a cluster. > What will happen if i am trying to an aggregation operation like (AVERAGE). > How will that work?? > Yes. > I have seen operations as SUM and COUNT. > How will the Query execution tree look like in case of an AVERAGE > It will look exactly like a SUM or COUNT except that two numbers will be accumulated instead of one. > 2. > Does the Resource model is optimized when compared to MapReduce. > Yes. This will happen because multiple levels of aggregation can be done in one tree without the barrier between map and reduce imposed by the MapReduce structure.
