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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1585) Allow to control how payloads are merged
Date Fri, 07 May 2010 05:47:49 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1585?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12865035#action_12865035
] 

Shai Erera commented on LUCENE-1585:
------------------------------------

I see that in trunk, SegmentMerger does not get IW in its ctor, and there are a couple of
places which call that ctor. So perhaps to not affect it, I'll add another ctor which takes
a PC/PP (whatever name we decide on), and the current one will delegate to it w/ null? Or
... I can have SM's ctor accept IW and take whatever it needs from it. Comparing it to 3x,
it will work exactly the same, only will obtain Directory, TermIndexInterval and CodecProvider
from IW.

What do you think?

> Allow to control how payloads are merged
> ----------------------------------------
>
>                 Key: LUCENE-1585
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1585
>             Project: Lucene - Java
>          Issue Type: New Feature
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Shai Erera
>            Priority: Minor
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-1585_3x.patch, LUCENE-1585_3x.patch, LUCENE-1585_trunk.patch
>
>
> Lucene handles backwards-compatibility of its data structures by
> converting them from the old into the new formats during segment
> merging. 
> Payloads are simply byte arrays in which users can store arbitrary
> data. Applications that use payloads might want to convert the format
> of their payloads in a similar fashion. Otherwise it's not easily
> possible to ever change the encoding of a payload without reindexing.
> So I propose to introduce a PayloadMerger class that the SegmentMerger
> invokes to merge the payloads from multiple segments. Users can then
> implement their own PayloadMerger to convert payloads from an old into
> a new format.
> In the future we need this kind of flexibility also for column-stride
> fields (LUCENE-1231) and flexible indexing codecs.
> In addition to that it would be nice if users could store version
> information in the segments file. E.g. they could store "in segment _2
> the term a:b uses payloads of format x.y".

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