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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