[ http://issues.apache.org/jira/browse/LUCENE-532?page=comments#action_12448780 ] Michael McCandless commented on LUCENE-532: -------------------------------------------
Also: I like the idea of never doing "seek" when writing. The less functionality we rely on from the filesystem, the more portable Lucene will be. Since Lucene is so wonderfully simple, never using "seek" during write is in fact very feasible. I think to do this we need to change the CFS file format, so that the offsets are stored at the end of the file. We actually can't pre-compute where the offsets will be because we can't make assumptions about how the file position changes when bytes are written: this is implementation specific. For example, if the Directory implementation does on-the-fly compression, then the file position will not be the number of bytes written. So I think we have to write at the end of the file. Any opinions or other suggestions? > [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. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://issues.apache.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
