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Posted to dev@lucene.apache.org by "Andrzej Bialecki (JIRA)" <ji...@apache.org> on 2010/04/07 00:57:34 UTC
[jira] Created: (LUCENE-2373) Change StandardTermsDictWriter to
work with streaming and append-only filesystems
Change StandardTermsDictWriter 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: 3.1
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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[jira] Commented: (LUCENE-2373) Change StandardTermsDictWriter to
work with streaming and append-only filesystems
Posted by "Earwin Burrfoot (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/LUCENE-2373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854254#action_12854254 ]
Earwin Burrfoot commented on LUCENE-2373:
-----------------------------------------
And then IndexOutput.seek() can be deleted. Cool.
> Change StandardTermsDictWriter 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: 3.1
>
>
> 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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[jira] Commented: (LUCENE-2373) Change StandardTermsDictWriter to
work with streaming and append-only filesystems
Posted by "Shai Erera (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/LUCENE-2373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855877#action_12855877 ]
Shai Erera commented on LUCENE-2373:
------------------------------------
I'd rather not count on file length as well ... so a put/getTermDictSize method on Codec will allow one to implement it however one wants, if running on HDFS for example?
> Change StandardTermsDictWriter 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: 3.1
>
>
> 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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[jira] Commented: (LUCENE-2373) Change StandardTermsDictWriter to
work with streaming and append-only filesystems
Posted by "Andrzej Bialecki (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/LUCENE-2373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854240#action_12854240 ]
Andrzej Bialecki commented on LUCENE-2373:
-------------------------------------------
Just noticed that the same problem exists in SimpleStandardTermsIndexWriter, and I propose the same solution there.
> Change StandardTermsDictWriter 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: 3.1
>
>
> 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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You can reply to this email to add a comment to the issue online.
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[jira] Commented: (LUCENE-2373) Change StandardTermsDictWriter to
work with streaming and append-only filesystems
Posted by "Michael McCandless (JIRA)" <ji...@apache.org>.
[ https://issues.apache.org/jira/browse/LUCENE-2373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854409#action_12854409 ]
Michael McCandless commented on LUCENE-2373:
--------------------------------------------
I would love to make Lucene truly write once (and moreve IndexOutput.seek), but... this approach makes me a little nervous...
In some environments, relying on the length of the file to be accurate might be risky: it's metadata, that can be subject to different client-side caching than the file's contents. EG on NFS I've seen issues where the file length was stale yet the file contents were not.
Maybe we could offer a separate codec that takes this approach, for use on filesystems like HDFS that can't seek during write? We should refactor standard codec so that "where this long gets stored" can be easily overridden by a subclass.
Or, alternatively, we could write this "index of the index" to a separate file?
> Change StandardTermsDictWriter 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: 3.1
>
>
> 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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You can reply to this email to add a comment to the issue online.
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