Hi Vidur, I'm not following. The "overwrite" flag causes the file to be overwritten starting at offset 0 - it doesn't allow you to retain any bit of the preexisting file. It's equivalent to a remove followed by a create. Think of it like O_TRUNC.
-Todd On Mon, Jun 21, 2010 at 10:03 PM, Vidur Goyal <vi...@students.iiit.ac.in>wrote: > Dear Todd, > > By truncating i meant removing unused *blocks* from the namespace and let > them be garbage collected. There will be no truncation of the last > block(even if it is not full). This way , rather then garbage collecting > all the blocks of a file , we will only be garbage collecting the > remaining blocks. > > -vidur > > > > HDFS assumes in hundreds of places that blocks never shrink. So, there is > > no > > option to truncate a block. > > > > -Todd > > > > On Mon, Jun 21, 2010 at 9:41 PM, Vidur Goyal > > <vi...@students.iiit.ac.in>wrote: > > > >> Hi All, > >> > >> In FSNamesystem#startFileInternal , whenever there is a overwrite flag > >> set > >> , why is the INode removed from the namespace and a new > >> INodeFileUnderConstruction is created. Why can't we use the convert the > >> same INode to INodeFileUnderConstruction. And we start writing to the > >> same > >> blocks at the same datanodes (after incrementing the GS) followed by > >> either truncating the remaining blocks(if the file size decreases) or > >> allocating new blocks (if the file size increases). This will decrease > >> data redundancy and the job of garbage collector and will increase > >> security. > >> > >> vidur > >> > >> > >> > >> > >> -- > >> This message has been scanned for viruses and > >> dangerous content by MailScanner, and is > >> believed to be clean. > >> > >> > > > > > > -- > > Todd Lipcon > > Software Engineer, Cloudera > > > > -- > > This message has been scanned for viruses and > > dangerous content by MailScanner, and is > > believed to be clean. > > > > > > > -- > This message has been scanned for viruses and > dangerous content by MailScanner, and is > believed to be clean. > > -- Todd Lipcon Software Engineer, Cloudera
