Because when you do select * the query just has to read and return the resultl but when you give query under query suffle sort and comparison happens thats why mapreduce...
*Warm Regards_**∞_* * Shashwat Shriparv* [image: http://www.linkedin.com/pub/shashwat-shriparv/19/214/2a9]<http://www.linkedin.com/pub/shashwat-shriparv/19/214/2a9>[image: https://twitter.com/shriparv] <https://twitter.com/shriparv>[image: https://www.facebook.com/shriparv] <https://www.facebook.com/shriparv>[image: http://google.com/+ShashwatShriparv] <http://google.com/+ShashwatShriparv>[image: http://www.youtube.com/user/sShriparv/videos]<http://www.youtube.com/user/sShriparv/videos>[image: http://profile.yahoo.com/SWXSTW3DVSDTF2HHSRM47AV6DI/] <shrip...@yahoo.com> On Fri, Feb 14, 2014 at 4:15 PM, Nitin Pawar <nitinpawar...@gmail.com>wrote: > when you are writing a file, it will need an application to create and > write the file. > Thats why the mapreduce job to create the file. > > Where as for other way when its displayed on console, its just hdfs cat > operation > > > On Fri, Feb 14, 2014 at 4:13 PM, Sreenath <sreenaths1...@gmail.com> wrote: > >> i have two queries >> 1. select * from tab1 limit 3; >> this returns the 3 rows quickly withoput launcing any map reduce jobs; >> >> 2. INSERT OVERWRITE LOCAL DIRECTORY "/tmp/query1/" select * from tab1 >> limit 3; >> but the same above query to write to a local directory launches a map >> reduce job and scans through all the rows launching map-reduce jobs >> >> why the differenceinexecution of both queries? >> >> -- >> Sreenath S Kamath >> Bangalore >> Ph No:+91-9590989106 >> > > > > -- > Nitin Pawar >
