[HADOOP-9864] Adopt SLF4Js over commons-logging

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 3.0.0-alpha1
• Assignee: Unassigned
• Reporter: Steve Loughran
• Created: 12/Aug/13 17:32
• Updated: 03/Nov/17 12:29
• Resolved: 03/Nov/17 12:29

Description

This is fairly major, but it's something to raise. Commons-logging is used as frozen front end to log4j with a pre-java5-varargs syntax, forcing us to wrap every log event with an if (log.isDebugEnabled() clause.

SLF4J

1. is the new de-facto standard Java logging API
2. does use varags for on-demand stringification {{log.info("routing to {}
   , host)}}
3. bridges to Log4J
4. hooks up direct to logback, which has a reputation for speed through less lock contention
5. still supports the same isDebugEnabled() probes, so commons-logging based classes could switch to SLF4J merely by changing the type of the LOG class.

Hadoop already depends on SLF4J for jetty support, hadoop-auth uses it directly.

This JIRA merely proposes making a decision on whether to adopt SL4J -and if so, how to roll it out.

The least-disruptive roll-out strategy would be to mandate it on new modules, then switch module-by-module in the existing code.
We'd also need to find all those tests that dig down to log4j directly, and make sure that they can migrate to the new APIs.

Issue Links

• is related to: HADOOP-8391 Hadoop-auth should use log4j