Hongbin: Please go through HRegion#doMiniBatchMutation(). You will see the connection of wal.append() and the WAL sync in step 7.
Cheers On Mon, Feb 16, 2015 at 6:05 AM, Dave Latham <lat...@davelink.net> wrote: > Hi Hongbin, > > The WAL class is used internally to the region server. Typically an HBase > write operation will first call WAL.append() with the data, then later, > after releasing locks, call WAL.sync() to ensure that the data for that > write has been synced to be durable before returning to the client (unless > the client instructed it to skip that step). > > Dave > > On Mon, Feb 16, 2015 at 5:21 AM, hongbin ma <mahong...@apache.org> wrote: > > > hi, all > > > > It seems WAL.append() in hbase, the javadoc says: > > > > * * Append a set of edits to the WAL. The WAL is not flushed/sync'd after > > this transaction* > > * * completes BUT on return this edit must have its region > edit/sequence > > id assigned* > > * * else it messes up our unification of mvcc and sequenceid. On > return > > <code>key</code> will* > > * * have the region edit/sequence id filled in.* > > > > This is really confusing me, if it does does flushed every update is > > instantly to disk, how can hbase ensures the WAL contains everything that > > was appended? What is hbase's philosophy in this? Does it allow some > degree > > of data loss? > > > > > > thanks > > hongbin > > >
