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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-735) Simple tool to back-convert from lockless to pre-lockless file format
Date Thu, 30 Nov 2006 11:54:21 GMT
Simple tool to back-convert from lockless to pre-lockless file format
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                 Key: LUCENE-735
                 URL: http://issues.apache.org/jira/browse/LUCENE-735
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Index
    Affects Versions: 2.1
            Reporter: Michael McCandless
         Assigned To: Michael McCandless
            Priority: Minor
             Fix For: 2.1
         Attachments: LUCENE-735.patch


Simple tool to back-convert from lockless to pre-lockless file format

The changes for lockless commits (LUCENE-701 ) are fairly minor and so
creating a tool to convert a lockless format index back to a
pre-lockless format index is 1) fairly simple, and 2) useful at least
for brave souls who want to try lockless but have the freedom to roll
back to Lucene 2.0, using the same index, if anything goes wrong.

I will attach an initial patch.

This has not yet received extensive testing so please be extremely
careful if you use this in production!  I've only done minimal testing
so far: using IndexFiles to produce an index under lockless,
converting it to pre-lockless, and then doing searches against that
index with 2.0.  More testing is clearly needed to ensure separate
deletes, separate norms, etc, are working correctly.

The tool prints details of what it did, eg:

  >> java org.apache.lucene.index.ConvertPreLockless index

  3 segments in index
  segment 0: not compound file format
    has deletions
    rename _a_2.del to _a.del
    no separate norms
  segment 1: not compound file format
    has deletions
    rename _b_1.del to _b.del
    no separate norms
  segment 2: not compound file format
    has deletions
    rename _c_1.del to _c.del
    no separate norms
  wrote "segments" file
  rename segments_8 to segments_8.old

Caveats:

  * Tread very carefully!  Test first in a sandox, etc.

  * Make sure you only run this tool on an index that is not in use by
    any reader/writers, else you could have problems: the tool
    currently does not acquire the write lock even though it's
    modifying the index.

  * On Windows only: if your index has any un-referenced files (ie,
    files that should have been deleted but were in use at the time)
    at the time you run this tool, then they will never be deleted
    (ie, pre-lockless Lucene won't know to delete them).



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