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From "Andrzej Bialecki (JIRA)" <>
Subject [jira] Commented: (LUCENE-2373) Change StandardTermsDictWriter to work with streaming and append-only filesystems
Date Fri, 07 May 2010 13:40:51 GMT


Andrzej Bialecki  commented on LUCENE-2373:

Good point, Lance - though for larger indexes the number of blocks (hence the number of sub-readers
in your scenario) would be substantial, maybe too high. Hadoop doesn't do much of local caching
of remote blocks, but I implemented a HDFS Directory in Luke that uses ehcache, and it works
quite well.

> Change StandardTermsDictWriter to work with streaming and append-only filesystems
> ---------------------------------------------------------------------------------
>                 Key: LUCENE-2373
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Andrzej Bialecki 
>             Fix For: 4.0
> Since early 2.x times Lucene used a skip/seek/write trick to patch the length of the
terms dict into a place near the start of the output data file. This however made it impossible
to use Lucene with append-only filesystems such as HDFS.
> In the post-flex trunk the following code in StandardTermsDictWriter initiates this:
> {code}
>     // Count indexed fields up front
>     CodecUtil.writeHeader(out, CODEC_NAME, VERSION_CURRENT); 
>     out.writeLong(0);                             // leave space for end index pointer
> {code}
> and completes this in close():
> {code}
>       out.writeLong(dirStart);
> {code}
> I propose to change this layout so that this pointer is stored simply at the end of the
file. It's always 8 bytes long, and we known the final length of the file from Directory,
so it's a single additional seek(length - 8) to read it, which is not much considering the

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