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https://issues.apache.org/jira/browse/LUCENE-5101?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13707889#comment-13707889
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Robert Muir commented on LUCENE-5101:
-------------------------------------
{quote}
Maybe we could use these numbers to have better defaults in CWF? (and only use
FixedBitSet for dense sets for example)
{quote}
+1: we should have better defaults. Ideally we would use DISI.cost() to
estimate the sparsity.
One problem is a lot of the costly filters that people want to cache have a
crap cost() implementation.
e.g. MultiTermQueryWrapperFilter could instead getAndSet() and return a DISI
with an actual accurate cost().
Or instead for now, we could also check firstDocID too...
> make it easier to plugin different bitset implementations to
> CachingWrapperFilter
> ---------------------------------------------------------------------------------
>
> Key: LUCENE-5101
> URL: https://issues.apache.org/jira/browse/LUCENE-5101
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Robert Muir
>
> Currently this is possible, but its not so friendly:
> {code}
> protected DocIdSet docIdSetToCache(DocIdSet docIdSet, AtomicReader reader)
> throws IOException {
> if (docIdSet == null) {
> // this is better than returning null, as the nonnull result can be
> cached
> return EMPTY_DOCIDSET;
> } else if (docIdSet.isCacheable()) {
> return docIdSet;
> } else {
> final DocIdSetIterator it = docIdSet.iterator();
> // null is allowed to be returned by iterator(),
> // in this case we wrap with the sentinel set,
> // which is cacheable.
> if (it == null) {
> return EMPTY_DOCIDSET;
> } else {
> /* INTERESTING PART */
> final FixedBitSet bits = new FixedBitSet(reader.maxDoc());
> bits.or(it);
> return bits;
> /* END INTERESTING PART */
> }
> }
> }
> {code}
> Is there any value to having all this other logic in the protected API? It
> seems like something thats not useful for a subclass... Maybe this stuff can
> become final, and "INTERESTING PART" calls a simpler method, something like:
> {code}
> protected DocIdSet cacheImpl(DocIdSetIterator iterator, AtomicReader reader) {
> final FixedBitSet bits = new FixedBitSet(reader.maxDoc());
> bits.or(iterator);
> return bits;
> }
> {code}
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