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https://issues.apache.org/jira/browse/SOLR-15630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17416347#comment-17416347
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ASF subversion and git services commented on SOLR-15630:
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Commit b0a4b0213016bef59fcc6a280c498cbf35e64230 in solr's branch
refs/heads/main from Chris M. Hostetter
[ https://gitbox.apache.org/repos/asf?p=solr.git;h=b0a4b02 ]
SOLR-15630: Logging MDC values no longer include a hardcoded prefix, allowing
custom logging configurations access to the plain values.
The default log4j2.xml PatternLayout has been updated to ensure the values are
formatted with the existing prefixes.
> 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
> Priority: Major
> Attachments: SOLR-15630.patch, SOLR-15630.patch, SOLR-15630.patch
>
>
> Prior to Solr 9, Solr code included hardcoded, single character, prefixes on
> all MDC values passed to the logging framework.
> Starting with Solr 9, these hardcoded prefixes have been removed, and the
> Logging "appends" are expected to provide any labeling/prefixing of what the
> values are. The default Solr log4j configuration has been updated to include
> the same single character prefixes (that were previously hardcoded).
> Users who have a custom log4j configuration that wish to ensure Solr 9.x logs
> are consistently formatted after upgrading will need to make similar changes
> to their logging configuration files, by using {{%notEmpty}} macro patterns
> that include the prefixes, and wrapping those around the existing {{%X}} MDC
> patterns:
> {code:title=8.x}
> [%X{collection} %X{shard} %X{replica} %X{core}]
> {code}
> {code:title=9.x}
> [%notEmpty{c:%X{collection}}%notEmpty{ s:%X{shard}}%notEmpty{
> r:%X{replica}}%notEmpty{ x:%X{core}}]
> {code}
> ----
> {panel:title=Original Description}
> 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)
> {panel}
>
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