Re: New logging system ideas

Ondřej Kuzník wrote:
> 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.

Yes, that's exactly what https://git.openldap.org/openldap/openldap/-/merge_requests/358 does.

> 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.

The reason we're discussing rotate functionality is because of a requirement that no other
system dependencies are needed. So, we can't just tell people to use logrotate.

Also, freopen() is not async-signal-safe and so isn't legal inside a signal handler. Nor is it
clear that freopen() is atomic within a threaded program. As such, you would still need at
least a mutex.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/