- Greatly enhanced rsyslogd's filw write performance by disabling file

    syncing capability of output modules by default. This feature is
    usually not required, not useful and an extreme performance hit (both
    to rsyslogd as well as the system at large). Unfortunately, most users
    enable it by default, because it was most intuitive to enable it in
    plain old sysklogd syslog.conf format. There is now a new config
    setting which must be enabled in order to support syncing. By default
    it is off. So even if the old-format config lines request syncing, it
    is not done unless explicitely enabled. I am sure this is a very useful
    change and not a risk at all. I need to think if I undo it under
    compatibility mode, but currently this does not happen (I fear a lot of
    lazy users will run rsyslogd in compatibility mode, again bringing up
    this performance problem...).
- added $ActionfileEnableSync config directive

1 files changed, 18 insertions, 1 deletions

diff --git a/doc/v3compatibility.html b/doc/v3compatibility.html
index b17aca82..c2a51139 100644
--- a/doc/v3compatibility.html
+++ b/doc/v3compatibility.html
@@ -87,7 +87,24 @@ via rsyslog.conf. That set of configuration directives is to be
 expanded. So far, we support:</p>
 <p>$klogSymbolsTwice [on/off]<br>
 $DebugPrintKernelSymbols [on/off] # spits *a lot* of messages at startup</p>
-<h2>Queue Modes for the Main Message Queue</h2>
+<h2>Output File Syncing</h2>Rsyslogd tries to keep as compatible to
+stock syslogd as possible. As such, it retained stock syslogd's default
+of syncing every file write if not specified otherwise (by placing a
+dash in front of the output file name). While this was a useful feature
+in past days where hardware was much less reliable and UPS seldom, this
+no longer is useful in today's worl. Instead, the syncing is a high
+performace hit. With it, rsyslogd writes files around 50 *times* slower
+than without it. It also affects overall system performance due to the
+high IO activity. In rsyslog v3, syncing has been turned off by
+default. This is done via a specific configuration directive
+"$ActionFileEnableSync on/off" which is off by default. So even if
+rsyslogd finds sync selector lines, it ignores them by default. In
+order to enable file syncing, the administrator must specify
+"$ActionFileEnableSync on" at the top of rsyslog.conf. This ensures
+that syncing only happens in those installations where the
+administrator actually wanted that (performance-intense) feature. In
+the fast majority of cases (if not all), this dramatically increases
+rsyslogd performance without any negative effects.<h2>Queue Modes for the Main Message Queue</h2>
 <p>Either "FixedArray" or "LinkedList" is recommended. "Direct"
 is available, but should not be used except for a very good reason
 ("Direct" disables queueing and will potentially lead to message loss