bq. Hbase uses append operation in hdfs to store/log WAL. Following append operation, hdfs sync operation would be called for persistence.
FYI On Tue, Feb 25, 2014 at 10:05 AM, Dhaval Shah <[email protected]>wrote: > Inline > > Regards, > Dhaval > > > ________________________________ > From: Upendra Yadav <[email protected]> > To: [email protected] > Sent: Tuesday, 25 February 2014 1:00 PM > Subject: Need some information over WAL > > > I have also doubt over WAL(write ahead log). > > In hdfs we can write a new file or we can append to old file. > > Is that correct : > 1. WAL only logs operations not its data... just like disk journaling(ext4) > - No WAL is a log of all new data, not just the operations > > 2. In case of Region Server failure... WAL replay will depends on Client to > get each operation's data that yet not committed/flushed to hdfs. > - No client will not generally know of a region server failure. It gets > the data from the WAL and replays it. The client may not even exist when a > region server crashes > > 3. Hbase uses append operation in hdfs to store/log WAL. > - Yes > > Thanks...
