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https://issues.apache.org/jira/browse/LUCENE-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699166#action_12699166
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Mark Miller commented on LUCENE-831:
------------------------------------

Thinking a bit on this this morning:

I think that will work out right. We would have 3 different attacks at 
ValueSource.

1. A ValueSource per segment reader that handles all default ValueSource needs 
- you get it with IndexReader.getValueSource. Its an UninversionValueSource 
wrapped by a CachingValueSource by default.

2. A singleton back compat value source that is wrapped by 
CacheByReaderValueSource. It has extra methods that takes Uninverters, allowing 
custom Uninverters and caching by Uninverter.

3. You can override the ValueSource used for Sorting by attaching it to the 
SortField. Likely, you would weap in a CacheByReaderValueSource and have your 
own singleton.

I think that gives us back compat and the best of both worlds?

> Complete overhaul of FieldCache API/Implementation
> --------------------------------------------------
>
>                 Key: LUCENE-831
>                 URL: https://issues.apache.org/jira/browse/LUCENE-831
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Hoss Man
>            Assignee: Mark Miller
>             Fix For: 3.0
>
>         Attachments: ExtendedDocument.java, fieldcache-overhaul.032208.diff, 
> fieldcache-overhaul.diff, fieldcache-overhaul.diff, 
> LUCENE-831-trieimpl.patch, LUCENE-831.03.28.2008.diff, 
> LUCENE-831.03.30.2008.diff, LUCENE-831.03.31.2008.diff, LUCENE-831.patch, 
> LUCENE-831.patch, LUCENE-831.patch, LUCENE-831.patch, LUCENE-831.patch, 
> LUCENE-831.patch, LUCENE-831.patch, LUCENE-831.patch, LUCENE-831.patch, 
> LUCENE-831.patch, LUCENE-831.patch, LUCENE-831.patch
>
>
> Motivation:
> 1) Complete overhaul the API/implementation of "FieldCache" type things...
>     a) eliminate global static map keyed on IndexReader (thus
>         eliminating synch block between completley independent IndexReaders)
>     b) allow more customization of cache management (ie: use 
>         expiration/replacement strategies, disk backed caches, etc)
>     c) allow people to define custom cache data logic (ie: custom
>         parsers, complex datatypes, etc... anything tied to a reader)
>     d) allow people to inspect what's in a cache (list of CacheKeys) for
>         an IndexReader so a new IndexReader can be likewise warmed. 
>     e) Lend support for smarter cache management if/when
>         IndexReader.reopen is added (merging of cached data from subReaders).
> 2) Provide backwards compatibility to support existing FieldCache API with
>     the new implementation, so there is no redundent caching as client code
>     migrades to new API.

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