[logback-user] FileAppender#setBufferedIO

Holger Hoffstaette holger.hoffstaette at googlemail.com
Sat Aug 14 11:32:10 CEST 2010

On Fri, 13 Aug 2010 12:57:22 +0200, Lars Fischer wrote:

> I would like to switch from Log4J to Logback. The old system extended
> Log4J FileAppender and used a method "setBufferedIO".
> The Logback FileAppender has no such a method. Does it no longer buffer?

>From http://logback.qos.ch/manual/appenders.html#OutputStreamAppender:

"Given the structure of current hard drives and performance tests we have
conducted, it appears that turning off immediate flushing or buffering of
character to byte conversions have rather small impact on performance. As
such, as of logback vesion 0.9.19, the ImmediateFlush, BufferedIO and
BufferSize properties have been removed without replacement."


I got curious and indeed it seems that the underlying file stream
implementation does no buffering, presumably to allow for recovery.
However by default it does not fsync on every event, so even though you
pay the OS system call and file locking (!) overhead, the OS/drive etc.
will likely still buffer anyway. In my experience buffering at least the
usual 4KB (pagesize) before writing can help a lot; log event output is
typically a lot shorter than that.

Interestingly I remember from a few years back that *some* people with
lots of logs on high-traffic web sites sometimes got better throughput
from unbuffered writes (contrary to everybody's expectation), whereas
most others said buffering was absolutely necessary and a great


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