Hi, the secondary namenode only fetches the two files when a checkpointing is needed.
Kai Am 06.10.2011 um 08:45 schrieb shanmuganathan.r: > Hi Kai, > > In the Second part I meant > > > Is the secondary namenode also contain the FSImage file or the two > files(FSImage and EdiltLog) are transferred from the namenode at the > checkpoint time. > > > Thanks > Shanmuganathan > > > > > > ---- On Thu, 06 Oct 2011 11:37:50 +0530 Kai Voigt<[email protected]> wrote > ---- > > > Hi, > > you're correct when saying the namenode hosts the fsimage file and the edits > log file. > > The fsimage file contains a snapshot of the HDFS metadata (a filename to > blocks list mapping). Whenever there is a change to HDFS, it will be appended > to the edits file. Think of it as a database transaction log, where changes > will not be applied to the datafile, but appended to a log. > > To prevent the edits file growing infinitely, the secondary namenode > periodically pulls these two files, and the namenode starts writing changes > to a new edits file. Then, the secondary namenode merges the changes from the > edits file with the old snapshot from the fsimage file and creates an updated > fsimage file. This updated fsimage file is then copied to the namenode. > > Then, the entire cycle starts again. To answer your question: The namenode > has both files, even if the secondary namenode is running on a different > machine. > > Kai > > Am 06.10.2011 um 07:57 schrieb shanmuganathan.r: > > > > > Hi All, > > > > I have a doubt in hadoop secondary namenode concept . Please correct if > the following statements are wrong . > > > > > > The namenode hosts the fsimage and edit log files. The secondary > namenode hosts the fsimage file only. At the time of checkpoint the edit log > file is transferred to the secondary namenode and the both files are merged, > Then the updated fsimage file is transferred to the namenode . Is it correct? > > > > > > If we run the secondary namenode in separate machine , then both > machines contain the fsimage file . Namenode only contains the editlog file. > Is it true? > > > > > > > > Thanks R.Shanmuganathan > > > > > > > > > > > > > > -- > Kai Voigt > [email protected] > > > > > > > -- Kai Voigt [email protected]
