Deprecate "create" method in FSDirectory.getDirectory in favor of IndexWriter's "create" [LUCENE-773] #1848
Description
It's confusing that there is a create=true|false at the FSDirectory
level and then also another create=true|false at the IndexWriter
level. Which one should you use when creating an index?
Our users have been confused by this in the past:
http://www.gossamer-threads.com/lists/lucene/java-user/4792
I think in general we should try to have one obvious way to achieve
something (like Python: http://en.wikipedia.org/wiki/Python_philosophy).
And the fact that there are now two code paths that are supposed to do
the same (similar?) thing, can more easily lead to sneaky bugs. One
case of #1218 (already fixed in trunk but not past releases),
which inspired this issue, can happen if you send create=false to the
FSDirectory and create=true to the IndexWriter.
Finally, as of lockless commits, it is now possible to open an
existing index for "create" while readers are still using the old
"point in time" index, on Windows. (At least one user had tried this
previously and failed). To do this, we use the IndexFileDeleter class
(which retries on failure) and we also look at the segments file to
determine the next segments_N file to write to.
With future issues like #1785 even more "smarts" may be required
to know what it takes to "create" a new index into an existing
directory. Given that we have have quite a few Directory
implemenations, I think these "smarts" logically should live in
IndexWriter (not replicated in each Directory implementation), and we
should leave the Directory as an interface that knows how to make
changes to some backing store but does not itself try to make any
changes.
Migrated from LUCENE-773 by Michael McCandless (@mikemccand), resolved Jan 23 2007