Minor addition: bq. WAL is a single and common file for all regions on a region server
hbase:meta has its own WAL file. On Tue, Feb 25, 2014 at 10:22 AM, Dhaval Shah <prince_mithi...@yahoo.co.in>wrote: > yes WAL is a single and common file for all regions on a region server. > Yes to 1. > Re 2: HBase will roll over WAL files and eventually delete them when they > are no longer needed. > > Regards, > Dhaval > > > ________________________________ > From: Upendra Yadav <upendra1...@gmail.com> > To: user@hbase.apache.org; Dhaval Shah <prince_mithi...@yahoo.co.in> > Sent: Tuesday, 25 February 2014 1:18 PM > Subject: Re: Need some information over WAL > > > Thanks Dhawal.... > > Oh... whatever i assumed with reading documents (partially).... that was > wrong... > > With ur answer... i have another questions... > WAL is a single and common file for all region of a Region server. > > Is this correct: > 1. So all operation(including data) will go to WAL... operation by > operation.... > > 2. Then on HDFS, HBase will have to perform delete operation on some set of > WAL files always... > > > > > On Tue, Feb 25, 2014 at 11:35 PM, Dhaval Shah > <prince_mithi...@yahoo.co.in>wrote: > > > Inline > > > > Regards, > > Dhaval > > > > > > ________________________________ > > From: Upendra Yadav <upendra1...@gmail.com> > > To: user@hbase.apache.org > > 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... >
