Yes, it need not keep an edits (transactions) stream locally cause those are passed synchronously to the BackupNameNode, which persists it on its behalf.
On Sun, Apr 7, 2013 at 1:21 PM, Lin Ma <lin...@gmail.com> wrote: > Thanks Harsh, > > For your comments, "What it means is that the NameNode need not store > anything locally", you mean Primary Name Node do not need to store > checkpoint/journal locally, and only need to keep memory image up-to-date > for edits? > > regards, > Lin > > > On Sun, Apr 7, 2013 at 3:31 PM, Harsh J <ha...@cloudera.com> wrote: >> >> Hi Lin, >> >> My reply inline. >> >> On Sun, Apr 7, 2013 at 12:36 PM, Lin Ma <lin...@gmail.com> wrote: >> > Hi guys, >> > >> > I am reading from this paper to learn about backup nodes >> > (http://www.storageconference.org/2010/Papers/MSST/Shvachko.pdf), >> > >> > It is mentioned, "It contains all file system metadata information >> > except >> > for block locations. It can perform all operations of the regular >> > NameNode >> > that do not involve modification of the namespace or knowledge of block >> > locations. ", what kinds of operations do not need knowledge of block >> > locations? >> >> Operations that do not involve data reads or writes would not require >> knowledge of block locations. Applying also the restriction of no >> namespace mutation, an example would be listing directories and >> looking up file information via FileStatus objects (perhaps the only >> examples - its like a safemode but no reads either). >> >> > It is also mentioned, "Use of a BackupNode provides the option of >> > running >> > the NameNode without persistent storage, delegating responsibility for >> > the >> > namespace state persisting to the BackupNode.", what means "running the >> > NameNode without persistent storage" and "delegating responsibility for >> > the >> > namespace state persisting"? >> >> What it means is that the NameNode need not store anything locally, >> but can rely on the edits being stored at the BackupNameNode which >> would continuously be receiving it. When restarted, it can grab a >> current checkpoint from the BNN and boot up anywhere, since there's no >> local storage requirement. >> >> -- >> Harsh J > > -- Harsh J
