[jira] [Created] (LUCENE-7375) Can we allow FSDirectory subclasses to customize whether the ctor does a mkdir?

["Michael McCandless (JIRA)" <ji...@apache.org>]

Michael McCandless created LUCENE-7375:
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             Summary: Can we allow FSDirectory subclasses to customize whether the ctor does a mkdir?
                 Key: LUCENE-7375
                 URL: https://issues.apache.org/jira/browse/LUCENE-7375
             Project: Lucene - Core
          Issue Type: Improvement
            Reporter: Michael McCandless


Today, just instantiating an {{FSDirectory}} always brings the directory into existence, even if you will do no writes ({{createOutput}}).

We have gone back and forth on this, over the ages.  E.g. see LUCENE-16 (only 2 digits there!!), LUCENE-773 (only 3 digits there!!), LUCENE-1464.  At one point we created the directory lazily, on the first write ({{createOutput}}) attempt, but now we always create it when you instantiate {{FSDirectory}}.

This causes some hassle for consumers, e.g. in https://github.com/elastic/elasticsearch/pull/19338 ES is forking {{SimpleFSDirectory}} in order to have a read-only directory impl.

Maybe we can do the {{Files.createDirectories}} in protected method that a subclass could override?




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