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https://issues.apache.org/jira/browse/LUCENE-3082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030528#comment-13030528
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Michael McCandless commented on LUCENE-3082:
--------------------------------------------
Patch looks great!
The segmentsToOptimize ought to contain every segment in the index; that's only
present for the case where optimize() is called in a bg thread but other
threads continue to index new documents causing new segments to be flushed.
These new segments would then NOT be in the segmentsToOptimize when the
optimize merges need to cascade.
TODO: for the command-line tool, we should make sure the index only has a
single commit point (ie, abort if not). Upgrading an index with more than one
commit point is hairy (I think it's fine not to support this case... but we
should not remove the commits).
> Add index upgrade method to IndexWriter to force an upgrade of all segments
> to last recent supported index format without optimizing
> ------------------------------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-3082
> URL: https://issues.apache.org/jira/browse/LUCENE-3082
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Index
> Reporter: Uwe Schindler
> Priority: Minor
> Fix For: 3.2, 4.0
>
> Attachments: LUCENE-3082.patch, LUCENE-3082.patch,
> index.31.optimized.cfs.zip, index.31.optimized.nocfs.zip
>
>
> Currently if you want to upgrade an old index to the format of your current
> Lucene version, you have to optimize your index or use
> addIndexes(IndexReader...) [see LUCENE-2893] to copy to a new directory. The
> optimize() approach fails if your index is already optimized.
> I propose to add a method to IndexWriter thats similar to optimize(), that
> uses a custom MergePolicy to upgrade all segments to the last format. This
> MergePolicy could simply also ignore all segments already up-to-date. All
> segments in prior formats would be merged to a new segment. The tool could
> optionally also optimize the index.
> This issue is different from LUCENE-2893, as it would only support upgrading
> indexes from previous Lucene versions in-place using the official path. Its a
> tool for the end user, not a developer tool.
> This addition should also go to Lucene 3.x, as we need to make users with
> pre-3.0 indexes go the step through 3.x, else they would not be able to open
> their index with 4.0. With this tool in 3.x the users could safely upgrade
> their index without relying on optimize to work on already-optimized indexes.
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