That's great dhruba, I guess the sooner it could go in is 0.21.1? J-D
On Wed, Jan 13, 2010 at 8:51 AM, Dhruba Borthakur <dhr...@gmail.com> wrote: > I opened http://issues.apache.org/jira/browse/HDFS-895 for this one. > > thanks, > dhruba > > On Tue, Jan 12, 2010 at 9:41 PM, Joydeep Sarma <jsensa...@gmail.com> wrote: > >> this is internal to the dfsclient. this would explain why performance >> would suck with queue threshold of 1. >> >> leave it up to Dhruba to explain the details. >> >> On Tue, Jan 12, 2010 at 9:16 PM, stack <st...@duboce.net> wrote: >> > On Tue, Jan 12, 2010 at 9:12 PM, stack <st...@duboce.net> wrote: >> > >> >> > any IO to a HDFS-file (appends, writes, etc) ae actually blocked on a >> >> > pending sync. "sync" in HDFS is a pretty heavyweight operation as it >> >> stands. >> >> >> >> i think this is likely to explain limited throughput with the default >> >> write queue threshold of 1. if the appends cannot make progress while >> >> one is waiting for the sync - then the write pipeline is going to be >> >> idle most of the time (with queue threshold of 1). >> >> >> >> i think it would be good to have the sync not block other writers on >> >> the file/pipeline. logically - it's not clear why it needs to (since >> >> the sync is just a wait for the completion as of some write >> >> transaction id - allowing new ones to be queued up subsequently). >> > >> > >> > Are you talking about internal to DFSClient Joydeep? Or some >> > synchronization block up in hlog? >> > >> > St.Ack >> > >> > > > > -- > Connect to me at http://www.facebook.com/dhruba >
