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]
