SequenceFile.Writer#syncFs is in Hadoop 1.0.0 (actually since 0.20.205), which calls the underlying FSDataOutputStream#sync which is actually hflush semantically (data not durable in case of data center wide power outage). hsync implementation is not yet in 2.0. HDFS-744 just brought hsync in trunk.
__Luke On Fri, May 25, 2012 at 9:30 AM, Harsh J <ha...@cloudera.com> wrote: > Mohit, > > Not if you call sync (or hflush/hsync in 2.0) periodically to persist > your changes to the file. SequenceFile doesn't currently have a > sync-API inbuilt in it (in 1.0 at least), but you can call sync on the > underlying output stream instead at the moment. This is possible to do > in 1.0 (just own the output stream). > > Your use case also sounds like you may want to simply use Apache Flume > (Incubating) [http://incubator.apache.org/flume/] that already does > provide these features and the WAL-kinda reliability you seek. > > On Fri, May 25, 2012 at 8:24 PM, Mohit Anchlia <mohitanch...@gmail.com> wrote: >> We get click data through API calls. I now need to send this data to our >> hadoop environment. I am wondering if I could open one sequence file and >> write to it until it's of certain size. Once it's over the specified size I >> can close that file and open a new one. Is this a good approach? >> >> Only thing I worry about is what happens if the server crashes before I am >> able to cleanly close the file. Would I lose all previous data? > > > > -- > Harsh J
