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Date: Thu, 26 May 2011 22:07:19 -0700 Message-ID: Subject: Re: Are hadoop fs commands serial or parallel From: Mapred Learn To: common-user@hadoop.apache.org, mapreduce-user@hadoop.apache.org, cdh-user@cloudera.org Content-Type: multipart/alternative; boundary=001636e0ac5282211c04a43ae9b4 --001636e0ac5282211c04a43ae9b4 Content-Type: text/plain; charset=ISO-8859-1 Hi guys, Another question related to it is that when you do hadoop fs -copyFromLocal or use API to call fs.write(), does it write to local filesystem first before writing to HDFS. I read and found out that it writes on local file-system until block-size is reached and then writes on HDFS. Wouldn't HDFS Client choke if it writes to local filesystem if multiple such fs -copyFromLocal commands are running. I thought atleast in fs.write(), if you provide byte array, it should not write on local file-system ? Could somebody tell how fs -copyFromLocal and fs.write() work ? Do they write on local-filesystem beofre block size is reached and then write to HDFS or write directly to HDFS ? Thanks in advance, -JJ On Wed, May 18, 2011 at 9:39 AM, Patrick Angeles wrote: > kinda clunky but you could do this via shell: > > for $FILE in $LIST_OF_FILES ; do > hadoop fs -copyFromLocal $FILE $DEST_PATH & > done > > If doing this via the Java API, then, yes you will have to use multiple > threads. > > On Wed, May 18, 2011 at 1:04 AM, Mapred Learn >wrote: > > > Thanks harsh ! > > That means basically both APIs as well as hadoop client commands allow > only > > serial writes. > > I was wondering what could be other ways to write data in parallel to > HDFS > > other than using multiple parallel threads. > > > > Thanks, > > JJ > > > > Sent from my iPhone > > > > On May 17, 2011, at 10:59 PM, Harsh J wrote: > > > > > Hello, > > > > > > Adding to Joey's response, copyFromLocal's current implementation is > > serial > > > given a list of files. > > > > > > On Wed, May 18, 2011 at 9:57 AM, Mapred Learn > > > wrote: > > >> Thanks Joey ! > > >> I will try to find out abt copyFromLocal. Looks like Hadoop Apis write > > > serially as you pointed out. > > >> > > >> Thanks, > > >> -JJ > > >> > > >> On May 17, 2011, at 8:32 PM, Joey Echeverria > wrote: > > >> > > >>> The sequence file writer definitely does it serially as you can only > > >>> ever write to the end of a file in Hadoop. > > >>> > > >>> Doing copyFromLocal could write multiple files in parallel (I'm not > > >>> sure if it does or not), but a single file would be written serially. > > >>> > > >>> -Joey > > >>> > > >>> On Tue, May 17, 2011 at 5:44 PM, Mapred Learn < > mapred.learn@gmail.com> > > > wrote: > > >>>> Hi, > > >>>> My question is when I run a command from hdfs client, for eg. hadoop > > fs > > >>>> -copyFromLocal or create a sequence file writer in java code and > > append > > >>>> key/values to it through Hadoop APIs, does it internally > > transfer/write > > > data > > >>>> to HDFS serially or in parallel ? > > >>>> > > >>>> Thanks in advance, > > >>>> -JJ > > >>>> > > >>> > > >>> > > >>> > > >>> -- > > >>> Joseph Echeverria > > >>> Cloudera, Inc. > > >>> 443.305.9434 > > >> > > > > > > -- > > > Harsh J > > > --001636e0ac5282211c04a43ae9b4--