[SOLR-11934] Visit Solr logging, it's too noisy.

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 8.6
• Assignee: Erick Erickson
• Reporter: Erick Erickson
• Created: 01/Feb/18 03:44
• Updated: 28/Jul/20 19:46
• Resolved: 09/May/20 17:17

Description

I think we have way too much INFO level logging. Or, perhaps more correctly, Solr logging needs to be examined and messages logged at an appropriate level.

We log every update at an INFO level for instance. But I think we log LIR at INFO as well. As a sysadmin I don't care to have my logs polluted with a message for every update, but if I'm trying to keep my system healthy I want to see LIR messages and try to understand why.

Plus, in large installations logging at INFO level is creating a LOT of files.

What I want to discuss on this JIRA is
1> What kinds of messages do we want log at WARN, INFO, DEBUG, and TRACE levels?
2> Who's the audience at each level? For a running system that's functioning, sysops folks would really like WARN messages that mean something need attention for instance. If I'm troubleshooting should I turn on INFO? DEBUG? TRACE?

So let's say we get some kind of agreement as to the above. Then I propose three things
1> Someone (and probably me but all help gratefully accepted) needs to go through our logging and assign appropriate levels. This will take quite a while, I intend to work on it in small chunks.
2> Actually answer whether unnecessary objects are created when something like log.info("whatever {}", someObjectOrMethodCall); is invoked. Is this independent on the logging implementation used? The SLF4J and log4j seem a bit contradictory.
3> Maybe regularize log, logger, LOG as variable names, but that's a nit.

As a tactical approach, I suggest we tag each LoggerFactory.getLogger in files we work on with //SOLR-(whatever number is assigned when I create this). We can remove them all later, but since I expect to approach this piecemeal it'd be nice to keep track of which files have been done already.

Finally, I really really really don't want to do this all at once. There are 5-6 thousand log messages. Even at 1,000 a week that's 6 weeks, even starting now it would probably span the 7.3 release.

This will probably be an umbrella issue so we can keep all the commits straight and people can volunteer to "fix the files in core" as a separate piece of work (hint).

There are several existing JIRAs about logging in general, let's link them in here as well.

Let the discussion begin!

Issue Links

• is related to: SOLR-11901 Improve how logging collects class name information
• is related to: SOLR-7887 Upgrade Solr to use log4j2 -- log4j 1 now officially end of life
• relates to: SOLR-11884 find/fix inefficiencies in our use of logging
• relates to: SOLR-14686 Remove log "[coreName]" (logid) which is redundant with MDC
• links to: GitHub Pull Request #1492