I think adding the abstraction layer and making it not only pluggable, but configurable would be great.
It would be nice to be able to tie into a service that logs directly to disk, rather than go through HDFS giving some potentially awesome speedup at the cost of having to write a logging service that handles replication, etc. Side note, Accumulo is using their own service to storing the WAL, rather than HDFS and I suspect that plays a big role in people's claim of its ability to do 'outperform' HBase. -Jesse Yates On Sat, Oct 1, 2011 at 2:04 PM, Stack <[email protected]> wrote: > Yes. For sure. Would need to check that the split can deal w/ > multiple logs written by the one server concurrently (sort by sequence > edit id after sorting on all the rest that makes up a wal log key). > > St.Ack > > On Sat, Oct 1, 2011 at 1:36 PM, karthik tunga <[email protected]> > wrote: > > Hey, > > > > Doesn't multiple WALs need some kind of merging when recovering from a > crash > > ? > > > > Cheers, > > Karthik > > > > > > On 1 October 2011 15:17, Stack <[email protected]> wrote: > > > >> +1 on making WAL pluggable so we can experiment. Being able to write > >> multiple WALs at once should be easy enough to do (the WAL split code > >> should be able to handle it). Also a suggestion made a while back was > >> making it so hbase could be configured to write two filesystems -- > >> there'd be hbase.rootdir as now -- and then we'd allow specifying > >> another fs to use for writing WALs (If not specified, we'd just use > >> hbase.rootdir for all filesystem interactions as now). > >> > >> St.Ack > >> > >> On Sat, Oct 1, 2011 at 10:56 AM, Dhruba Borthakur <[email protected]> > >> wrote: > >> > I have been experimenting with the WAL settings too. It is obvious > that > >> > turning off the wal makes ur transactions go faster, HDFS write/sync > are > >> not > >> > yet very optimized for high throughput small writes. > >> > > >> > However, irrespective of whether I have one wal or two, I have seeing > the > >> > same throughput. I have experimented with an HDFS setting that allows > >> > writing/sync to multiple replicas in parallel, and that has increased > >> > performance for my test workload, see > >> > https://issues.apache.org/jira/browse/HDFS-1783. > >> > > >> > About using one wal or two, it will be nice if we can separate out the > >> wal > >> > API elegantly and make it pluggable. In that case, we can experiment > >> HBase > >> > with multiple systems. Once we have it pluggable, we can make the > habse > >> wal > >> > go to a separate HDFS (pure SSD based maybe?). > >> > > >> > -dhruba > >> > > >> > > >> > On Sat, Oct 1, 2011 at 8:09 AM, Akash Ashok <[email protected]> > >> wrote: > >> > > >> >> Hey, > >> >> I've see that setting writeToWAL(false) boosts up the writes like > crazy. > >> I > >> >> was just thinking having MuiltipleWAL on HBase. I understand that > this > >> is a > >> >> consideration in BigTable paper that a WAL per region is not used > >> because > >> >> it > >> >> might result in a lot of disk seeks when there are large number of > >> reasons. > >> >> But how about having as many WALs as the number of HardDrives in the > >> >> system. > >> >> I see that the recommended configs for HBase are 4 - 12 hard drives > per > >> >> node. This might kick the writes up a notch. > >> >> > >> >> Would like to know the general opinion on this one? > >> >> > >> >> Cheers, > >> >> Akash A > >> >> > >> > > >> > > >> > > >> > -- > >> > Connect to me at http://www.facebook.com/dhruba > >> > > >> > > >
