Thanks Azuryy! So, when a write is successful to the WAL on the responsible region server, in fact that means that the write was committed to 3 total DataNodes, correct?
On Mon, Jun 10, 2013 at 5:37 PM, Azuryy Yu <[email protected]> wrote: > yes. datanode write is pipeline. and only if pipeline writing finished, dn > return ok. > > --Send from my Sony mobile. > On Jun 11, 2013 8:27 AM, "Lucas Stanley" <[email protected]> wrote: > > > Hi, > > > > In the Strata 2013 training lectures, Jonathan Hsieh from Cloudera said > > something about HBase syncs which I'm trying to understand further. > > > > He said that HBase sync guarantees only that a write goes to the local > disk > > on the region server responsible for that region and in-memory copies go > on > > 2 other machines in the HBase cluster. > > > > But I thought that when the write goes to the WAL on the first region > > server, that the HDFS append would push that write to 3 machines total in > > the HDFS cluster. In order for the append write to the WAL to be > > successful, doesn't the DataNode on that machine have to pipeline the > write > > to 2 other DataNodes? > > > > I'm not sure what Jonathan was referring to when he said that 2 in-memory > > copies go to other HBase machines? Even when the memstore on the first > > region server gets full, doesn't the flush to the HFile get written on 3 > > HDFS nodes in total? > > >
