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? >
