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https://issues.apache.org/jira/browse/LUCENE-831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649180#action_12649180
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Alex Vigdor commented on LUCENE-831:
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Another useful feature that seems like it would be pretty easy to implement on
top of this patch is cache warming; that is, the ability to reopen an
IndexReader and repopulate its caches before making it "live". The main thing
missing is a Cache.getKeys() method which could be used to discover what caches
are already in use, in order to repopulate them after reopening the
IndexReader. This cache warming could be performed externally to the
IndexReader (by calling getCacheData for each of the keys after reopening), or
perhaps the reopen method could be overloaded with a boolean "reloadCaches" to
perform this in the same method call.
The rationale for this I hope is clear; my application, like many I'm sure,
keeps a single IndexReader for handling searches, and in a separate thread from
search request handling commits writes and reopens the IndexReader before
replacing the IndexReader reference for new searches (reference counting is
then used to eventually close the old reader instances). It would be ideal for
that separate thread to also bear the expense of cache warming; even with this
patch against our 4 GB indices, along with -Duse.object.array.sort=true, a
search request coming immediately after reopening the index will pause 20-40
seconds while the caches refill. Preferably that could be done in the
background and request handling threads would never be slowed down.
> 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
> Fix For: 3.0
>
> Attachments: fieldcache-overhaul.032208.diff,
> fieldcache-overhaul.diff, fieldcache-overhaul.diff,
> 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
>
>
> 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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