Uwe Schindler created LUCENE-10342:
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Summary: Add (very limited) java.util.logging to Lucene Core
Key: LUCENE-10342
URL: https://issues.apache.org/jira/browse/LUCENE-10342
Project: Lucene - Core
Issue Type: New Feature
Components: core/other
Reporter: Uwe Schindler
Assignee: Uwe Schindler
At the moment we have some parts in Lucene where we check for features of the
JDK and use them, only if available:
- We only use MMapDirectory, if we can unmap, so sun.misc.Unsafe must be
available
- To correctly calculate heap space requirements of data structures for caching
and other types of buffers, we try to calculate the heap size of objects. To do
this correctly we need some information like the size of ordinal object
pointers. If they are 32 bits on 64 bit platforms, the memory usage of Object[]
arrays (and HashSet/HashMaps) dramatically reduce size by factor of 2.
As those checks require "optional" modules in the java module system, which may
not even be available by default as they are unsupported, we do the check
dynamically.
With the Java module system the problems start, that a user of Lucene may need
to add those modules to the module descriptor of the application. If he misses
that or for some other reason it does not work (like feature is not available),
we silently disable MMapDirectory or for memory usage we may be off by an
factor of 2.
My suggestion is now to enable java.util.logging in Lucene's core (maybe also
in other modules, too - luke is already) and report such warnings using
java.util.logging. Any downstream code will see the logging then depending on
the used logging system (log4j, slf4j with correct wrapper module).
I know this suggestion may cause a bit a flame war because of disagreement
about pros and cons about if logging is needed, so I'd like to limit this to
warnings+. We won't ever emit info/debug/trace. To make sure we only log "warn"
and "error"/"severe" events, I will add a forbiddenapis rule to deny all other
loglevels.
As a side effect I will also add an IndexWriter log stream implementation for
java.util.logging to make it easy to log infostream events during indexing.
I will provide a PR adding 2 warnings and the InfoStream implementation.
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