yes, 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
--Send from my Sony mobile. On Jun 11, 2013 8:40 AM, "Lucas Stanley" <[email protected]> wrote: > 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? > > > > > >
