50ms is believable. hsync makes each DN call fsync and wait for acks, so you'd expect at least a disk seek time (~10ms) with some extra time depending on how much unsync'd data is being written.
So, just as some back of the envelope math, assuming a disk that can write at 100MB/s: 50ms - 10ms seek = 40ms writing time 100 MB/s * 40ms = 4MB If you're hsync'ing every 4MB, 50ms would be exactly what I'd expect. Best, Andrew On Sat, Aug 24, 2013 at 10:11 PM, haosdent <haosd...@gmail.com> wrote: > Hi, all. Hadoop support hsync which would call fsync of system after > 2.0.2. I have tested the performance of hsync() and hflush() again and > again, but I found that the hsync call() everytime would spent nearly 50ms > while the hflush call() just spent 2ms. In this slide( > http://www.slideshare.net/enissoz/hbase-and-hdfs-understanding-filesystem-usagePage > 18), the author mentions that hsync() is 2x slower than hflush(). So, > is anything wrong? Thank you very much and looking forward to your help. > > -- > Best Regards, > Haosong Huang > Sent with Sparrow (http://www.sparrowmailapp.com/?sig) > >
