Re: New logging system ideas

On Wed, Jul 14, 2021 at 03:40:35PM +0100, Howard Chu wrote:
> Howard Chu wrote:
>> Just some initial thoughts on what a new logging daemon should do for us:
> 
> Scaling back to something easier for now:
> 
> We'll use the existing Debug msgs as-is. The olcLogFile directive will specify the
> path of a local logging file to write to. Currently, writing to this logfile is
> controlled by the -d debuglevel flags, not the -s sysloglevel flags. When a logfile
> is configured, debug messages go to both stderr and the logfile.
> 
> We'll add a new option olcLogFileOnly (boolean), which will force messages to only
> go to the logfile (and skip writing any to stderr). Since the point of using the
> local file logging facility is for performance, it will be desirable to avoid this
> double-writing of messages.
> 
> We'll add an olcLogFileRotate option that specifies a logfile maxsize and rotation
> interval, in megabytes and hours, respectively. Any message that would cause the
> current logfile to exceed the specified size will cause the file to be closed/rotated/reopened.
> Any message that arrives after the specified number of hours will do likewise.
> Rotated files will be renamed to <logfile>.YYYYMMDDHHMM.

This sounds too complicated, you'd need to measure time and/or size
written everywhere and all the time.

Solutions already exist that do this and everyone knows how to use them:
logrotate(8). We just need to register a signal (SIGHUP or SIGUSR1 are
used most often) and freopen(3) the stderr stream in the handler. No
locks needed, job done.

> Supporting this rotation functionality will require a mutex around the logger function,
> so it's possible that we still won't gain back much performance going down this route.
> 
> Possibly the parameter should include another field for max # of logfiles to retain,
> I haven't really thought about that yet.
> 
> Comments?