[gpfsug-discuss] Confusing I/O Behavior

[Peter Serocka]

Let’s keep in mind that line buffering is a concept 
within the standard C library;
if every log line triggers one write(2) system call,
and it’s not direct io, then multiple write still get
coalesced into few larger disk writes (as with the dd example).

A logging application might choose to close(2)
a log file after each write(2) — that produces
a different scenario, where the file system might
guarantee that the data has been written to disk 
when close(2) return a success. 

(Local Linux file systems do not do this with default mounts,
but networked filesystems usually do.)

Aaron, can you trace your application to see
what is going on in terms of system calls?

— Peter
  

> On 2018 Apr 10 Tue, at 18:28, Marc A Kaplan <makaplan at us.ibm.com> wrote:
> 
> Debug messages are typically unbuffered or "line buffered".   If that is truly causing a performance problem AND you still want to collect the messages -- you'll need to find a better way to channel and collect those messages.
> 
> 
> _______________________________________________
> gpfsug-discuss mailing list
> gpfsug-discuss at spectrumscale.org
> http://gpfsug.org/mailman/listinfo/gpfsug-discuss