[jira] [Created] (SOLR-15630) MDC "prefix labels" should be handled by Layout - not hardcoded in solr code

["Chris M. Hostetter (Jira)" <ji...@apache.org>]

Chris M. Hostetter created SOLR-15630:
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             Summary: MDC "prefix labels" should be handled by Layout - not hardcoded in solr code
                 Key: SOLR-15630
                 URL: https://issues.apache.org/jira/browse/SOLR-15630
             Project: Solr
          Issue Type: Improvement
      Security Level: Public (Default Security Level. Issues are Public)
            Reporter: Chris M. Hostetter
            Assignee: Chris M. Hostetter


Currently, when Solr puts values in the MDC for logging, it always prepends them with a "CHAR" + "COLON" prefix that uniquely identifies what the value is – even though the MDC is a map and every value has a "key" associated with it that identifies what it is, ex...
{code:java}
  public static void setCollection(String collection) {
    if (collection != null) {
      MDC.put(COLLECTION_PROP, "c:" + collection);
    } else {
      MDC.remove(COLLECTION_PROP);
    }
  }
{code}
This choice evidently traces back to when MDC values where initially added SOLR-6673/SOLR-7590 (when Solr was still using slf4j->JUL IIUC) because that was best (only?) way folks found to ensure that log messages that did _not_ have values for specific MDC keys weren't cluttered with valueless prefixes  even when a log message didn't correspond to a specific collection (or replica, or shard, etc...)

But with modern log4j, we can use use things like the {{%notEmpty}} syntax to prevent excessive verbosity when MDC values aren't set – allowing us to move the prefixes out of the Solr code and into Solr default log4j configuration – so that users who customize their log4j configuration with things like {{%mdc}} (or JSON logging) can get the "bare" values w/o hardcoded prefixes. (while keeping the exact same default log format ... or even improving it by removing some of the wasted whitespace)

 



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