Issue

Is asynchronous file logging supported with rsyslog?

A feature of rsyslog that allows you to skip syncing after every log entry is undocumented in the rsyslog.conf man page of RHEL6.4's rsyslog-5.8.10-6.el6 package. The feature is documented at http://www.rsyslog.com/doc/rsyslog_conf_actions.html:

You may prefix each entry with the minus '-' sign to omit syncing the file after every logging. Note that you might lose information if the system crashes right behind a write attempt. Nevertheless this might give you back some performance, especially if you run programs that use logging in a very verbose manner.

It seems that the version packaged does have this functionality. This can be verified by downloading and unpacking http://ftp.redhat.com/pub/redhat/linux/enterprise/6Server/en/os/SRPMS/rsyslog-5.8.10-6.el6.src.rpm. Once unpacked, examination of tools/omfile.c in the source directory, specifically lines 742 - 747, reveals some implements of the feature:

    if(*p == '-') {
        pData->bSyncFile = 0;
        p++;
    } else {
        pData->bSyncFile = bEnableSync;
    }