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https://issues.apache.org/jira/browse/LUCENE-2373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885022#action_12885022
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Michael McCandless commented on LUCENE-2373:
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bq. DefaultCodecProvider does exactly this. Or do you mean instead of using
abstract methods in CodecProvider?
Right, I meant move the default impls into CodecProvider, so an app with a
custom CodecProvider need not implement the defaults.
bq. The reading is already factored out, but the writing ... Well, it's just 8
bytes per segment ... the reason I didn't factor it out is that it would
require additional before/after delegation, or a replication of larger sections
of code...
I hear you, but it looks sort of hackish to factor out one part (seeking to the
dir) but not the other part (writing/reading the dirOffset); but I'm fine w/
committing it like this. Maybe just add a comment in
AppendingTermsDictReader.seekDir that dirOffset, which the writer had written
into header of file, is ignored?
> Create a Codec to work with streaming and append-only filesystems
> -----------------------------------------------------------------
>
> Key: LUCENE-2373
> URL: https://issues.apache.org/jira/browse/LUCENE-2373
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Andrzej Bialecki
> Fix For: 4.0
>
> Attachments: appending.patch
>
>
> 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.seek(CodecUtil.headerLength(CODEC_NAME));
> 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 benefits.
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