Re: SMP: logging

On 02/23/2010 07:44 AM, Kinkie wrote:
> 2010/2/23 Tsantilas Christos <chtsanti_at_users.sourceforge.net>:
>>> Log rotation will probably need special care to avoid rotating the same
>>> log many times. It is relatively easy to designate one process to do the
>>> rotation (e.g., squid1), but that alone is not enough to synchronize
>>> everything. Ideally, I would prefer to avoid locking. Any clever tricks
>>> applicable here?
>> Maybe something like the following:
>> - there is a master process
>> - master process communicates with one direction pipes with kids, sending
>> various commands
>>
>> For logs rotation:
>> - master process closes the old file and rename it
>> - master process opens a new log file
>> - kids still writing to the old file (because they did not close the
>> file descriptor yet)
>> - master process send a command to all kids saying that the log file
>> rotated
>> - The kids close the log file and reopen it.
>>
>> The above will work at least for unix systems (I do not know about
>> MS-Windows)
>> Master/kids communication using pipes is used by the apache worker server.
>> I am also using it in my icap server. I am not seeing any problem.
>
> Why not just having a log writing helper to whom clients write log
> lines via some kind of sockets?
> That would make the log rotation problem just go away - especially the
> part where there may be race conditions among workers writing together
> to the same file.

The logging daemon does not make log rotation problem go away. You still
need to implement log rotation. It just becomes slightly easier to do so.

The O_APPEND solution, if it works, does not have race conditions among
workers writing together to the same file. Or, more precisely, we trust
the file system layer to handle those race conditions.

Please see my earlier email with the same subject for the
daemon-vs-append comparison summary. I would not be surprised if there
are more pros and cons to consider here, but so far I do not see enough
advantages to implement a logging daemon as the default SMP logging
mechanism.

Thank you,

Alex.
Received on Tue Feb 23 2010 - 16:04:18 MST