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https://issues.apache.org/jira/browse/LUCENE-3531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13168812#comment-13168812
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Uwe Schindler commented on LUCENE-3531:
---------------------------------------
I did some investigation. If you want a complete WeakIdentityHashMap witha all
iterators and so on its heavy to do and you must in all cases also wrap all
keys with a WeakReference even for lookup (unless you implement your completely
own HashMap impl). The easy fix here is to use a wrapper "Reference" object as
cache key, that simply has a final field and equals/hashCode that does the
system hashcode. By comparing the wrapper object as key, two wrapper objects
are only equal, if the wrapped objects are identical:
{code:java}
static final class IdentityKeyWrapper<T> {
public final T key;
private final int hashCode;
public IdentityKeyWrapper(T key) {
this.key = key;
this.hashCode = System.identityHashCode(key);
}
public int hashCode() { return hashCode; }
public boolean equals(Object o) {
if (o == this) return true;
if (o instanceof IdentityKeyWrapper) {
return ((IdentityKeyWrapper<T>)o).key == this.key;
}
return false;
}
}
{code}
The backside is that you have to wrap the Bits interface even on a lookup, but
thats cheap just like boxing/unboxing (eden space).
> Improve CachingWrapperFilter to optionally also cache acceptDocs, if
> identical to liveDocs
> ------------------------------------------------------------------------------------------
>
> Key: LUCENE-3531
> URL: https://issues.apache.org/jira/browse/LUCENE-3531
> Project: Lucene - Java
> Issue Type: Improvement
> Components: core/search
> Affects Versions: 4.0
> Reporter: Uwe Schindler
> Assignee: Michael McCandless
> Fix For: 4.0
>
> Attachments: LUCENE-3531.patch
>
>
> Spinoff from LUCENE-1536: This issue removed the different cache modes
> completely and always applies the acceptDocs using
> BitsFilteredDocIdSet.wrap(), the cache only contains raw DocIdSet without any
> deletions/acceptDocs. For IndexReaders that are seldom reopened, this might
> not be as performant as it could be. If the acceptDocs==IR.liveDocs, those
> DocIdSet could also be cached with liveDocs applied.
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