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https://issues.apache.org/jira/browse/HADOOP-15007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16349144#comment-16349144
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Anu Engineer commented on HADOOP-15007:
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I think we are conflating different issues here into this JIRA. So first let us
separate the issues discussed until now and then discuss potential solutions.
# Excessive Logging for Unknown tags: We agree that we should reduce the volume
of logging, and we have two proposals here. First one, log only once for each
unknown tag. Second, Log only in the debug mode. Marton argues that logging in
debug mode is useless since no one would see this warning.
{{Proposed Solution: Log only once}}.
# Why do we have Enums instead of Strings: The reason is that we use these tags
as a set of known tags -- and use them in the code to display various
information to the end user. So it is a set of well-known strings. That is the
use case that enums are designed to solve, and it is easy for us to detect a
tag which we don't know off. Hence the excessive logging issue. I think if we
make it into strings, we will lose the ability even to warn, let us look for
three times or more for a specific string assumes people will not copy/paste
wrong tags. I submit that it is going to happen. So Enums are the best possible
way to detect this. With that, I agree that let us log only once for a tag that
we don't know off.
{{Proposed Solution: Convert this to strings or Keep Enums, but fix the
original logging issue.}}
# Hadoop Common should not have tags for HDFS and YARN: Now this is a new point
and something that I buy.
{{Proposed Solution: Load these Enums from the other jars -- and have a config
value that sets the name of the jars or some sort of a function that those JARs
can call to register these tags and it gets used. Let us do that as an
improvement to in a different JIRA.}}
if we are doing action item 3, then it is not relevant if we keep this as enums
or not. We still need the logging only once approach to make sure that tags
that we don't know of are warned only once. Does that work for everyone? if so
Ajay can start working on a patch.
> Stabilize and document Configuration <tag> element
> --------------------------------------------------
>
> Key: HADOOP-15007
> URL: https://issues.apache.org/jira/browse/HADOOP-15007
> Project: Hadoop Common
> Issue Type: Improvement
> Components: conf
> Affects Versions: 3.1.0
> Reporter: Steve Loughran
> Assignee: Ajay Kumar
> Priority: Blocker
>
> HDFS-12350 (moved to HADOOP-15005). Adds the ability to tag properties with a
> <tag> value.
> We need to make sure that this feature is backwards compatible & usable in
> production. That's docs, testing, marshalling etc.
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