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https://issues.apache.org/jira/browse/LUCENE-2133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12787718#action_12787718
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Christian Kohlschütter commented on LUCENE-2133:
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Mark, could you please name the changes you would like to be excluded?
I thought I had only included necessary changes.
Some dependent changes are not so obvious, but necessary.
For example, Analyzer.close now needs to throw an IOException because of
CloseableThreadLocal now closing an IOException because of doClose() throwing
an IOException because it may close references from an IndexCache that might
throw an IOException. Luckily this is covered by java.io.Closeable (which
declared #close() to throw an IOException), and Analyzer implements that
interface already.
> [PATCH] IndexCache: Refactoring of FieldCache, FieldComparator, SortField
> -------------------------------------------------------------------------
>
> Key: LUCENE-2133
> URL: https://issues.apache.org/jira/browse/LUCENE-2133
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.9.1, 3.0
> Reporter: Christian Kohlschütter
> Attachments: LUCENE-2133-complete.patch, LUCENE-2133.patch,
> LUCENE-2133.patch
>
>
> Hi all,
> up to the current version Lucene contains a conceptual flaw, that is the
> FieldCache. The FieldCache is a singleton which is supposed to cache certain
> information for every IndexReader that is currently open
> The FieldCache is flawed because it is incorrect to assume that:
> 1. one IndexReader instance equals one index. In fact, there can be many
> clones (of SegmentReader) or decorators (FilterIndexReader) which all access
> the very same data.
> 2. the cache information remains valid for the lifetime of an IndexReader. In
> fact, some IndexReaders may be reopen()'ed and thus they may contain
> completely different information.
> 3. all IndexReaders need the same type of cache. In fact, because of the
> limitations imposed by the singleton construct there was no implementation
> other than FieldCacheImpl.
> Furthermore, FieldCacheImpl and FieldComparator are bloated by several static
> inner-classes that could be moved to package level.
> There have been a few attempts to improve FieldCache, namely LUCENE-831,
> LUCENE-1579 and LUCENE-1749, but the overall situation remains the same:
> There is a central registry for assigning Caches to IndexReader instances.
> I now propose the following:
> 1. Obsolete FieldCache and FieldCacheKey and provide index-specific,
> extensible cache instances ("IndexCache"). IndexCaches provide common caching
> functionality for all IndexReaders and may be extended (for example,
> SegmentReader would have a SegmentReaderIndexCache and store different data
> than a regular IndexCache)
> 2. Add the index-specific field cache (IndexFieldCache) to the IndexCache.
> IndexFieldCache is an interface just like FieldCache and may support
> different implementations.
> 3. The IndexCache instances may be flushed/closed by the associated
> IndexReaders whenever necessary.
> 4. Obsolete FieldCacheSanityChecker because no more "insanities" are expected
> (or at least, they do not impact the overall performance)
> 5. Refactor FieldCacheImpl and the related classes (FieldComparator,
> SortField)
> I have provided an patch which takes care of all these issues. It passes all
> JUnit tests.
> The patch is quite large, admittedly, but the change required several
> modifications and some more to preserve backwards-compatibility.
> Backwards-compatibility is preserved by moving some of the updated
> functionality in the package org.apache.lucene.search.fields (field
> comparators and parsers, SortField) while adding wrapper instances and
> keeping old code in org.apache.lucene.search.
> In detail and besides the above mentioned improvements, the following is
> provided:
> 1. An IndexCache specific for SegmentReaders. The two ThreadLocals are moved
> from SegmentReader to SegmentReaderIndexCache.
> 2. A housekeeping improvement to CloseableThreadLocal. Now delegates the
> close() method to all registered instances by calling an onClose() method
> with the threads' instances.
> 3. Analyzer.close now may throw an IOException (this already is covered by
> java.io.Closeable).
> 4. A change to Collector: allow IndexCache instead of IndexReader being
> passed to setNextReader()
> 5. SortField's numeric types have been replaced by direct assignments of
> FieldComparatorSource. This removes the "switch" statements and the
> possibility to throw IllegalArgumentExceptions because of unsupported type
> values.
> The following classes have been deprecated and replaced by new classes in
> org.apache.lucene.search.fields:
> - FieldCacheRangeFilter (=> IndexFieldCacheRangeFilter)
> - FieldCacheTermsFilter (=> IndexFieldCacheTermsFilter)
> - FieldCache (=> IndexFieldCache)
> - FieldCacheImpl (=> IndexFieldCacheImpl)
> - all classes in FieldCacheImpl (=> several package-level classes)
> - all subclasses of FieldComparator (=> several package-level classes)
> Final notes:
> - The patch would be simpler if no backwards compatibility was necessary. The
> Lucene community has to decide which classes/methods can immediately be
> removed, which ones later, which not at all. Whenever new classes depend on
> the old ones, an appropriate notice exists in the javadocs.
> - The patch introduces a new, deprecated class
> IndexFieldCacheSanityChecker.java which is just there for testing purposes,
> to show that no sanity checks are necessary any longer. This class may be
> removed at any time.
> - I expect that the patch does not impact performance. On the contrary, as
> the patch removes a few unnecessary checks we might even see a slight
> speedup. No benchmarking has been done so far, though.
> - I have tried to preserve the existing functionality wherever possible and
> to focus on the class/method structure only. We certainly may improve the
> caches' behavior, but this out of scope for this patch.
> - The refactoring finally makes the high duplication of code visible: For all
> supported atomic types (byte, double, float, int, long, short) three classes
> each are required: *Cache, *Comparator and *Parser. I think that further
> simplification might be possible (maybe using Java generics?), but I guess
> the current patch is large enough for now.
> Cheers,
> Christian
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