[jira] [Resolved] (LUCENE-9669) N-2 compatibility for file formats

["Simon Willnauer (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-9669?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Simon Willnauer resolved LUCENE-9669.
-------------------------------------
    Resolution: Fixed

> N-2 compatibility for file formats
> ----------------------------------
>
>                 Key: LUCENE-9669
>                 URL: https://issues.apache.org/jira/browse/LUCENE-9669
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Simon Willnauer
>            Assignee: Simon Willnauer
>            Priority: Major
>             Fix For: master (9.0)
>
>          Time Spent: 3.5h
>  Remaining Estimate: 0h
>
> Currently Lucene supports reading and writing indices that have been
> created with the current or previous (N-1) version of Lucene. Lucene
> refuses to open an index created by N-2 or earlier versions.
> I would like to propose that Lucene adds support for opening indices
> created by version N-2 in read-only mode. Here's what I have in mind:
> - Read-only support. You can open a reader on an index created by
> version N-2, but you cannot open an IndexWriter on it, meaning that
> you can neither delete, update, add documents or force-merge N-2
> indices.
> - File-format compatibility only. File-format compatibility enables
> reading the content of old indices, but not more. Everything that is
> done on top of file formats like analysis or the encoding of length
> normalization factors is not guaranteed and only supported on a
> best-effort basis.
> The reason I came up with these limitations is because I wanted to
> make the scope minimal in order to retain Lucene's ability to move
> forward. If there is consensus to move forward with this, I would like
> to target Lucene 9.0 with this change.
> This is a follow-up of the mailinglist thread [here|http://mail-archives.apache.org/mod_mbox/lucene-dev/202101.mbox/%3CCAAHmpkg1BD9RtmVFR4jweYgYAXwz5OsY1hV9ubZkS0fHSFnTCQ@mail.gmail.com%3E] 



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