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From Igor Motov <>
Subject Re: ZooKeeper Logging
Date Fri, 26 Mar 2010 00:13:05 GMT
I agree, this is concerning. There is a similar situation with JCL in SOLR
1.4 (
With log4j-over-slf4j-X.Y.Z.jar in the .war file, whoever will need to
switch the logging system will have to make sure that an appropriate set of
*-over-slf4j and slf4j-* files is in the classpath.

So, it might make sense to change the last paragraph of to something like this:

Users who want an alternate logging implementation (log4j, logback, jcl,
etc) will need to repackage the .war file and replace slf4j-jdk14-X.Y.Z.jar
with an alternate implementation. They should also remove
jcl-over-slf4j-X.Y.Z.jar if they are switching to JCL and
log4j-over-slf4j-X.Y.Z.jar if they are using cloud branch and switching to
log4j. Having both jcl-over-slf4j and slf4j-jcl.jar or log4j-over-slf4j.jar
and slf4j-log4j.jar in the classpath may result in an infinite loop.

There is already a link to slf4j site on the page. But, it might be also
useful to add a link directly to the page that describes SLF4J bridges:


On Thu, Mar 25, 2010 at 4:26 PM, Mark Miller <> wrote:

> On 03/25/2010 11:27 AM, Mark Miller wrote:
>> On 03/25/2010 11:22 AM, Igor Motov wrote:
>>> I wonder if it would make sense to replace log4j-1.2.15.jar in the lib
>>> directory of the cloud branch with log4j-over-slf4j-1.5.5.jar. SOLR is
>>> already using SLF4J for its logging and log4j-over-slf4j bridge would
>>> redirect all ZooKeeper log messages into the same SLF4J logging stream. I
>>> did it in my setup and and it helped me a lot when I ran into issues with
>>> my
>>> ZooKeeper configuration.
>>> Thank you,
>>> Igor
>>>  Yeah, this is a great idea - been meaning to look into this since Uwe
>> mentioned to me that it was possible the other week. Hadn't realized these
>> bridge jars existed previously. Yonik had started looking into getting the
>> ZooKeeper project to switch to SLF4J, but this is a great solution for now.
> Hmm - I've done this for now - but this is going to need some good
> documentation at the least. It works great for Solr in it's default state
> (using util logging) - but you don't want this jar if you choose to use the
> log4j connector. Otherwise they loop back and forth with each other.
> --
> - Mark

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