[jira] Commented: (LUCENE-2474) Allow to plug in a Cache Eviction Listener to IndexReader to eagerly clean custom caches that use the IndexReader (getFieldCacheKey)

["Yonik Seeley (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-2474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12978371#action_12978371 ] 

Yonik Seeley commented on LUCENE-2474:
--------------------------------------

There's a lot of little issues here I think:
  - "close event" doesn't really describe the behavior since an event is not generated on every close of every reader as one might expect.
  - This implementation is problematic since higher level readers don't propagate the event listeners to subreaders... i.e. I need to walk the tree myself and add add a listener to every reader, and on a reopen() I would need to walk the tree again and add listeners only to the new readers that have a new coreKey.

We've talked before about putting caches directly on the readers - that still seems like the most straightforward approach?
We really need one cache that doesn't care about deletions, and one cache that does.

> Allow to plug in a Cache Eviction Listener to IndexReader to eagerly clean custom caches that use the IndexReader (getFieldCacheKey)
> ------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-2474
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2474
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Shay Banon
>         Attachments: LUCENE-2474.patch
>
>
> Allow to plug in a Cache Eviction Listener to IndexReader to eagerly clean custom caches that use the IndexReader (getFieldCacheKey).
> A spin of: https://issues.apache.org/jira/browse/LUCENE-2468. Basically, its make a lot of sense to cache things based on IndexReader#getFieldCacheKey, even Lucene itself uses it, for example, with the CachingWrapperFilter. FieldCache enjoys being called explicitly to purge its cache when possible (which is tricky to know from the "outside", especially when using NRT - reader attack of the clones).
> The provided patch allows to plug a CacheEvictionListener which will be called when the cache should be purged for an IndexReader.

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