-Re: Calling o/s.flush() in HLog.sync()?
Himanshu Vashishtha 2013-11-06, 01:22
Okay, good to know but not sure how your response is related to what I
On Tue, Nov 5, 2013 at 1:08 AM, Haosong Huang <[EMAIL PROTECTED]> wrote:
> An os fsync() call will spent nearly 10ms because of the harddisk iops
> neckbottle. A hsync() would become two os fsync(). One for checksum file
> and theother for block file. If you use SSD disk, you could try use fsync()
> instead of flush() and mount file system without writebarrier.
> 2013-11-5 下午1:12于 "Himanshu Vashishtha" <[EMAIL PROTECTED]>写道：
> > Looking at ProtobufLogWriter class, it looks like the call to flush() in
> > the sync method is a noop.
> > The underlying output stream is DFSOutputStream, which doesn't implement
> > flush().
> > And, it calls sync() anyway, which ensures the data is written to DN's
> > (cache).
> > Previously with SequenceFile$Writer, it writes data to the outputstream
> > (using Writables#write), and invoke sync/hflush.
> > Is there a reason we have this call here? Please let me know if I miss
> > context.
> > Thanks,
> > Himanshu