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From: "Mak, Howard" <hmak@vaultus.com>
To: Log4J Users List <log4j-user@logging.apache.org>
Date: Mon, 17 Dec 2007 14:50:27 -0500
Subject: RE: parent logger to filter child logger by level
Thread-Topic: parent logger to filter child logger by level
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Thanks for your response.

Here is what I'm trying to achieve:

(1)     File A contains all logs
(2)     File B contains only the FATAL/ERROR/WARN logs in file A

In other words, (2) provides a bird's eye view of problems that can be easi=
ly missed when reading in (1) (which can be quite big).

Is my only option to write a filter-by-Level appender to be used by (1)?

- Howard

-----Original Message-----
From: Curt Arnold [mailto:carnold@apache.org]
Sent: Monday, December 17, 2007 14:40
To: Log4J Users List
Subject: Re: parent logger to filter child logger by level


On Dec 17, 2007, at 1:05 PM, Mak, Howard wrote:

> I'm trying to duplicate WARN logs to a separate file by using the
> below log4j.properties.
>
>        log4j.rootLogger       =3D WARN, <appender_1>
>        log4j.logger.MYLOG     =3D ALL, <appender_2>
>        log4j.additivity.MYLOG =3D true
>
> However, appender_1 contains more stuff than I want.
>
> Am I wrong to expect that rootlogger will filter out all logs other
> thatn MYLOG @ <WARN> or <ERROR>?

Yes.  appender_1 will should receive all logging requests with a level
of WARN or higher and any logging requests sent to the "MYLOG"
appender regardless of level.

There are two independent concepts, one is the effective level
threshold of a logger and the other is the destination of any logging
events that satisfy the effective level threshold.

The effective level of a logger is the level of its nearest ancestor
with an explicitly set level and rootLevel is the ultimate ancestor of
any logger.   So the "MYLOG" logger or any logger that starts "MYLOG."
will have an effective level of ALL (the lowest possible level) and
any other logger will have an effective level of WARN.

If a logging requests meets or exceeds the effective level of its
logger, then it is processed by every appender attached to the logger
and every ancestor stopping after it reaches the rootLogger or a
logger with additivity set to false.  The effective level of the
intermediary loggers do not affect propagation.  The default value for
additivity is true, so your configuration line that sets the value to
its default, while legal, is atypical.  If you wanted logging requests
that were sent to "MYLOG" or descendants to not be sent to appender_1,
then you should set additivity to false.

Specifically, the propagation logic would not check that a logging
request that propagated from MYLOG is WARN or higher.  The
independence of the effective level and propagation allows a user to
drop the threshold in a specific part of the logger hierarchy by
simply inserting a lower level at the point of concern.  It would be
very common for the rootLogger to have an INFO level and then some
descendant to be set to DEBUG or TRACE to get more detailed info.


> Am I confusing level inheritance down to children loggers vs. filter
> of children logs by parent loggers?  Is the latter not supported by
> Log4j?
>

Could you explain the end result you'd like to achieve?


> I'm using version 1.2.15.
>
> Thanks for any help.
>
> - Howard
>
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