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51 lines
1.9 KiB
Plaintext
51 lines
1.9 KiB
Plaintext
Using log calls
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===============
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There are several hidden gotchas when using logging. The main
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problem is that certain patterns are evaluated and objects
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constructed even if the logging level is more restrictive
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than this call. If the logging level is WARN, then the following
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log.info patterns are evaluated and never-used objects are
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created even though the message is never logged.
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This can be very expensive as per measurements with Java Flight
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Recorder. It's particularly egregious when complex operations
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are performed for, say, log.debug or trace calls, which
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are rarely actually used.
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- log.info("some stuff " + "some other stuff") will concatenate the
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strings and create an object
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- log.info("some stuff {}", object.method()) will execute the
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method.
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- log.info("some stuff {}", object.toString()) will execute
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the toString and then throw the results away.
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-----------
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NOTES:
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- If you're creating a logging call that has no choice but to
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do something expensive, surround it with "if (log.is*Enabled)".
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- Logging calls can take a bare exception, but do not
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use the braces if you want the stack trace! So
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log.info("stuff {}", exception) will not print the full stack,
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log.info("stuff ", exception) _will_ print the full stack.
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log.inf0("stuff {} ", some_object, exception) will print the full stack.
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- When slf4j supports lambdas in logging calls (log4j2 does now),
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we can use lambdas rather than "if log.is*Enabled". slf4j 2.0
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will when released.
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- error and fatal level messages are NOT checked. However, if you want to
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check these levels for including '+', specify '-PcheckPlus=true'. This is more
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a style than functional check.
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For a fuller discussion, see LUCENE-7788 and the other JIRAs linked
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from there.
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Until we get all the calls cleaned up, you MUST specify -PsrcDir=relative_path,
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e.g. '-PsrcDir=solr/core/src/java/org/apache/solr/core'. This task will
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recursively check all '*.java. files under that directory.
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