Good to know! Please also consider improving the javadoc on that method to reflect this, by logging a doc JIRA under HDFS :)
On Thu, Apr 4, 2013 at 12:33 PM, Mei Long <lon...@gmail.com> wrote: > Harsh, > > Thank you! This is exactly what I was confused about. By looking at the code > I was suspecting that it's not looking at rack locality for the second > scenario (No DN on writer node.) But I was unable to confirm it without > running the code. > > Your answer makes so much sense. Thank you!! :-) I'm much happier now. > > On Thu, Apr 4, 2013 at 2:14 AM, Harsh J <ha...@cloudera.com> wrote: >> >> Hi Mei, >> >> These questions are best fit for the whole hdfs-dev@ group, which am >> adding while responding back. >> >> You're correct that the local node being not chosen, a random node on >> the same rack as the writer may be tried. However, if the writer node >> itself had no local DN in the first place, a completely random node >> across any rack may be selected. >> >> This is visible at >> >> http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java?view=markup >> (~263). >> >> On Thu, Apr 4, 2013 at 12:53 AM, Mei Long <lon...@gmail.com> wrote: >> > Hi Harsh, >> > >> > I found your post on JIRA regarding the comments. I find them very >> > confusing >> > as well. I'm trying to figure out the following comment: >> > >> > * the 1st replica is placed on the local machine, >> > * otherwise a random datanode. >> > >> > Do you know when it says "otherwise a random datanode," does it mean any >> > random datanode anywhere on the network or a random datanode on the same >> > rack as the local machine? I've been looking at the code for an hour and >> > I'm >> > getting more confused with the comment and code in chooseLocalNode() >> > >> > /* choose <i>localMachine</i> as the target. >> > >> > * if <i>localMachine</i> is not availabe, >> > >> > * choose a node on the same rack >> > >> > * @return the choosen node >> > >> > */ >> > >> > Your help is much appreciated! >> > >> > Mei >> >> >> >> -- >> Harsh J > > -- Harsh J
