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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4764) Faster but more RAM/Disk consuming DocValuesFormat for facets
Date Tue, 12 Feb 2013 15:01:20 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13576660#comment-13576660
] 

Robert Muir commented on LUCENE-4764:
-------------------------------------

{quote}
I'm still not sure what's the best (or common) way to work w/ Codecs. When do you create your
own FilterCodec and override the relevant method, and when are you expected to extend another
Codec?
{quote}

The rule is that an index needs to be self-describing: basically I should be able to open
any index if i have the right stuff in my classpath.

This would be somewhat of a burden for users who just want to change their "id" field to use
a different postings format (they would have to make a whole codec with their own unique name),
and so on.

So Lucene42Codec uses PerField[Postings/DocValuesFormat] (note this is final!), which separately
record the name of the format used on a per-field basis.

Because of this, its ok that it not final and exposes these hooks to custom postings/docvalues
per-field, because it writes the name of those formats into the index for the field.

                
> Faster but more RAM/Disk consuming DocValuesFormat for facets
> -------------------------------------------------------------
>
>                 Key: LUCENE-4764
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4764
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 4.2, 5.0
>
>         Attachments: LUCENE-4764.patch, LUCENE-4764.patch, LUCENE-4764.patch
>
>
> The new default DV format for binary fields has much more
> RAM-efficient encoding of the address for each document ... but it's
> also a bit slower at decode time, which affects facets because we
> decode for every collected docID.

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