@Bejoy Adding a little bit here,the ouput of map task writes first to a memory buffer, and when contents reaches a threshold a background thread will write the contents to disk.
Niranjan Singh On Wed, Apr 17, 2013 at 1:06 PM, Ramesh R Nair <rameshrkco...@gmail.com>wrote: > Hi Bejoy, > > Regarding the output of Map phase, does Hadoop store it in local fs or > in HDFS. > I believe it is in the former. Correct me if I am wrong. > > Regards > Ramesh > > > On Wed, Apr 17, 2013 at 10:30 AM, <bejoy.had...@gmail.com> wrote: > >> The data is in HDFS in case of WordCount MR sample. >> >> In hdfs, you have the metadata in NameNode and actual data as blocks >> replicated across DataNodes. >> >> In case of reducer, If a reducer is running on a particular node then you >> have one replica of the blocks in the same node (If there is no space >> issues) and rest replicas on other nodes. >> Regards >> Bejoy KS >> >> Sent from remote device, Please excuse typos >> ------------------------------ >> *From: * Raj Hadoop <hadoop...@yahoo.com> >> *Date: *Tue, 16 Apr 2013 21:49:34 -0700 (PDT) >> *To: *user@hadoop.apache.org<user@hadoop.apache.org> >> *ReplyTo: * user@hadoop.apache.org >> *Subject: *Basic Doubt in Hadoop >> >> Hi, >> >> I am new to Hadoop. I started reading the standard Wordcount program. I >> got this basic doubt in Hadoop. >> >> After the Map - Reduce is done, where is the output generated? Does the >> reducer ouput sit on individual DataNodes ? Please advise. >> >> >> Thanks, >> Raj >> > >
