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From Rainer Jung <>
Subject Re: Enhanced error log format for trunk?
Date Tue, 08 Jun 2010 21:10:20 GMT
On 08.06.2010 22:56, Stefan Fritsch wrote:
> On Monday 07 June 2010, Rainer Jung wrote:
>> On 03.06.2010 16:49, Stefan Fritsch wrote:
>>> On Tuesday 01 June 2010, Rainer Jung wrote:
>>>> 4) General correlation improvements
>>>> To be able to correlate error and access log, it would be
>>>> helpful to share a common id, e.g. the unique_id, and be able
>>>> to log it in both files. The id generated by mod_unique_id
>>>> comes too late though (post_read_request). Since it actually
>>>> only uses the request timestamp and the connection id of the
>>>> request, it could be calculated much earlier.
>>> I have thought about this before, but I wanted to get the
>>> per-module loglevel configuration into trunk first.
>>> The log id could be created by the first call to ap_log_rerror.
>>> If there has not been an errorlog entry for a request by the
>>> time of the log transaction hook, the corresponding field in the
>>> access log would just be "-".
>> That's an interesting idea, making it pretty trivial to filter
>> those lines, that have any error log entries.
>>> The function creating the log id could also log some interesting
>>> information once per request, instead of logging it for every log
>>> line. For example PID/TID, local+remote IP+Port, number of
>>> keep-alives on the connection, ...
>> Hmmm, but some basics should stay on each line, otherwise it's to
>> much hassle collection stuff (or we provide a script). Being able
>> to correlate between access and error log is nice, being forced to
>> correlate inside the error log to collect the data is not so nice.
> The script would be "grep log-id error_log". I fear the useful
> information depends very much on the situation. Logging everything
> makes sure that we have the useful information. But this would
> obviously flood the error log if we do it on every line or even for
> every request. Hence my suggestion to only log it for requests which
> have at least one other error log message logged.
> This should be configurable. Either this conditional verbose logging
> or the "some information in every line" style that we have now. And it
> should also be configurable what the "some information" should be.
>> Do you already have any code fragments for that?
> No, these are only ideas so far. I have thought of following things
> which may be nice to have as error log flags:
> - timestamp granularity
> - don't log to the error log file (useful for modules using the error
> log hook)
> - log some kind of unique id
> - do conditional verbose logging as outlined above
> - log the name of the module
> - always or never log source file name+line number, or make it depend
> on the log level like now
> - log process/thread id
> - log errors that are induced by the client at level error or at level
> debug (e.g. file not found, connection closed by client)
> Information that may be useful in the conditional verbose logging:
> - local/remote port+ip,
> - vhost/Host-header
> - some way to correlate which requests are on the same connection,
> like a connection id (I think pid/tid are not enough with mpm event,
> but I could be mistaken)


> - Referrer-header
> - number of keep-alive requests on the connection
> That's a lot, but I can think of situations where any of the above
> information would be useful. Actually, for most pieces I can remember
> situations where the information would have been useful.

What about introducing log formats for the error log, like 
mod_log_config does for the access log? Parsing the format string once 
and registering callbacks to do the actual formatting.

Naive implementation would mean a lot of code copying from mod_log_config.


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