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From Chris Hostetter <hossman_luc...@fucit.org>
Subject Re: [jira] Commented: (LUCENE-532) [PATCH] Indexing on Hadoop distributed file system
Date Sun, 30 Jul 2006 00:55:21 GMT

: This actually looks like a good and patch that doesn't break any tests.
: I'll commit it in the coming days, as it looks like it should be
: backwards compatible... except CFS won't be supported unless somebody
: patches that, too (I tried quickly and soon got unit tests to fail :( ).

The one thing the Unit tests can't verify is that the version checking is
working (ie: that the new code will still read old indexes properly).  The
patch looks fairly straight forward to me so I don't think that will be a
problem -- but you may want to try searching an index built with 2.0 after
you apply the patch just to sanity check it.

This will neccessitate "Lucene 2.1" being the next version released from
the trunk because of the file format change correct? ... i have no
objection to that, i just want to verify my understanding of the file
format versioning.



:
: > [PATCH] Indexing on Hadoop distributed file system
: > --------------------------------------------------
: >
: >                 Key: LUCENE-532
: >                 URL: http://issues.apache.org/jira/browse/LUCENE-532
: >             Project: Lucene - Java
: >          Issue Type: Improvement
: >          Components: Index
: >    Affects Versions: 1.9
: >            Reporter: Igor Bolotin
: >            Priority: Minor
: >         Attachments: indexOnDFS.patch, SegmentTermEnum.patch, TermInfosWriter.patch
: >
: >
: > In my current project we needed a way to create very large Lucene indexes on Hadoop
distributed file system. When we tried to do it directly on DFS using Nutch FsDirectory class
- we immediately found that indexing fails because DfsIndexOutput.seek() method throws UnsupportedOperationException.
The reason for this behavior is clear - DFS does not support random updates and so seek()
method can't be supported (at least not easily).
: >
: > Well, if we can't support random updates - the question is: do we really need them?
Search in the Lucene code revealed 2 places which call IndexOutput.seek() method: one is in
TermInfosWriter and another one in CompoundFileWriter. As we weren't planning to use CompoundFileWriter
- the only place that concerned us was in TermInfosWriter.
: >
: > TermInfosWriter uses IndexOutput.seek() in its close() method to write total number
of terms in the file back into the beginning of the file. It was very simple to change file
format a little bit and write number of terms into last 8 bytes of the file instead of writing
them into beginning of file. The only other place that should be fixed in order for this to
work is in SegmentTermEnum constructor - to read this piece of information at position = file
length - 8.
: >
: > With this format hack - we were able to use FsDirectory to write index directly to
DFS without any problems. Well - we still don't index directly to DFS for performance reasons,
but at least we can build small local indexes and merge them into the main index on DFS without
copying big main index back and forth.
:
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-Hoss


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