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https://issues.apache.org/jira/browse/LUCENE-2386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855889#action_12855889
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Earwin Burrfoot commented on LUCENE-2386:
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Meh, that all is just a matter of perspective.
It doesn't look weird for me that an empty commit happens. Go, create some SVN
repository - it has initial #0 commit inside. I bet all version control systems
and all databases have the concept of null initial commit.
This empty commit is what discerns empty existing directory from empty lucene
index. If you create some docs, index them, then delete and commit, you're
going to get just the same picture - a directory with a single segments* file
(only generation number will differ).
And references to "but from now on they are never modified" are just weird -
it's a Lucene index dammit, no files are ever modified here.
But, what looks *really* weird to me is suggestions like
bq. Then you can check easily if you should call open() (==null) or reopen
(otherwise). Or create a blank stub of IR which emulates an empty Dir, and when
reopen is called works well (if the Directory is not empty now) ...
adding complexity and workarounds to plug a hole that didn't exist before the
"fix" that does essentially nothing of value.
My question is still unanswered - what is the proper way (after this fix) to
open an IR over possibly-empty directory? My app, for example, opens an IR and
does scheduled reopens. The time interval is small, a reopen over unmodified
index is a noop, so this is all beautifully simple and just as effective as
waiting for a commit event (like I did in the past, just like you). It opens an
IndexWriter with CREATE_OR_APPEND mode before opening the first reader, and is
thus guaranteed to have a good index directory regardless of the situation.
Immediate fix I see is to check whether the directory is empty and do a first
empty commit myself - UGLY.
> IndexWriter commits unnecessarily on fresh Directory
> ----------------------------------------------------
>
> Key: LUCENE-2386
> URL: https://issues.apache.org/jira/browse/LUCENE-2386
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Reporter: Shai Erera
> Assignee: Shai Erera
> Fix For: 3.1
>
> Attachments: LUCENE-2386.patch, LUCENE-2386.patch, LUCENE-2386.patch,
> LUCENE-2386.patch, LUCENE-2386.patch
>
>
> I've noticed IndexWriter's ctor commits a first commit (empty one) if a fresh
> Directory is passed, w/ OpenMode.CREATE or CREATE_OR_APPEND. This seems
> unnecessarily, and kind of brings back an autoCommit mode, in a strange way
> ... why do we need that commit? Do we really expect people to open an
> IndexReader on an empty Directory which they just passed to an IW w/
> create=true? If they want, they can simply call commit() right away on the IW
> they created.
> I ran into this when writing a test which committed N times, then compared
> the number of commits (via IndexReader.listCommits) and was surprised to see
> N+1 commits.
> Tried to change doCommit to false in IW ctor, but it got IndexFileDeleter
> jumping on me .. so the change might not be that simple. But I think it's
> manageable, so I'll try to attack it (and IFD specifically !) back :).
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