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https://issues.apache.org/jira/browse/LUCENE-1483?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Mark Miller updated LUCENE-1483:
--------------------------------
Description:
This issue changes how an IndexSearcher searches over multiple segments. The
current method of searching multiple segments is to use a MultiSegmentReader
and treat all of the segments as one. This causes filters and FieldCaches to be
keyed to the MultiReader and makes reopen expensive. If only a few segments
change, the FieldCache is still loaded for all of them.
This patch changes things by searching each individual segment one at a time,
but sharing the HitCollector used across each segment. This allows FieldCaches
and Filters to be keyed on individual SegmentReaders, making reopen much
cheaper. FieldCache loading over multiple segments can be much faster as well -
with the old method, all unique terms for every segment is enumerated against
each segment - because of the likely logarithmic change in terms per segment,
this can be very wasteful. Searching individual segments avoids this cost. The
term/document statistics from the multireader are used to score results for
each segment.
When sorting, its more difficult to use a single HitCollector for each sub
searcher. Ordinals are not comparable across segments. To account for this, a
new sort enabled HitCollector is introduced that is able to collect and sort
across segments (because of its ability to compare ordinals across segments).
This TopFieldCollector class will collect the values/ordinals for a given
segment, and upon moving to the next segment, translate any ordinals/values so
that they can be compared against the values for the new segment. This is done
lazily.
All and all, the switch seems to provide numerous performance benefits, in both
sorted and non sorted search. We were seeing a good loss on indices with lots
of segments (1000?) and certain queue sizes / queries, but the latest results
seem to show thats been mostly taken care of (you shouldnt be using such a
large queue on such a segmented index anyway).
* Introduces
** MultiReaderHitCollector - a HitCollector that can collect across multiple
IndexReaders. Old HitCollectors are wrapped to support multiple IndexReaders.
** TopFieldCollector - a HitCollector that can compare values/ordinals across
IndexReaders and sort on fields.
** FieldValueHitQueue - a Priority queue that is part of the TopFieldCollector
implementation.
** FieldComparator - a new Comparator class that works across IndexReaders.
Part of the TopFieldCollector implementation.
** FieldComparatorSource - new class to allow for custom Comparators.
* Alters
** IndexSearcher uses a single HitCollector to collect hits against each
individual SegmentReader. All the other changes stem from this ;)
* Deprecates
** TopFieldDocCollector
** FieldSortedHitQueue
was:
This issue changes how an IndexSearcher searches over multiple segments. The
current method of searching multiple segments is to use a MultiSegmentReader
and treat all of the segments as one. This causes filters and FieldCaches to be
keyed to the MultiReader and makes reopen expensive. If only a few segments
change, the FieldCache is still loaded for all of them.
This patch changes things by searching each individual segment one at a time,
but sharing the HitCollector used across each segment. This allows FieldCaches
and Filters to be keyed on individual SegmentReads, making reopen much cheaper.
FieldCache loading over multiple segments can be much faster as well - with the
old method, all unique terms for every segment is enumerated against each
segment - because of the likely logarithmic change in terms per segment, this
can be very wasteful. Searching individual segments avoids this cost. The
term/document statistics from the multireader are used to score results for
each segment.
When sorting, its more difficult to use a single HitCollector for each sub
searcher. Ordinals are not comparable across segments. To account for this, a
new sort enabled HitCollector is introduced that is able to collect and sort
across segments (because of its ability to compare ordinals across segments).
This TopFieldCollector class will collect the values/ordinals for a given
segment, and upon moving to the next segment, translate any ordinals/values so
that they can be compared against the values for the new segment. This is done
lazily.
All and all, the switch seems to provide numerous performance benefits, in both
sorted and non sorted search. We were seeing a good loss on indices with lots
of segments (1000?) and certain queue sizes / queries, but the latest results
seem to show thats been mostly taken care of (you shouldnt be using such a
large queue on such a segmented index anyway).
* Introduces
** MultiReaderHitCollector - a HitCollector that can collect across multiple
IndexReaders. Old HitCollectors are wrapped to support multiple IndexReaders.
** TopFieldCollector - a HitCollector that can compare values/ordinals across
IndexReaders and sort on fields.
** FieldValueHitQueue - a Priority queue that is part of the TopFieldCollector
implementation.
** FieldComparator - a new Comparator class that works across IndexReaders.
Part of the TopFieldCollector implementation.
** FieldComparatorSource - new class to allow for custom Comparators.
* Alters
** IndexSearcher uses a single HitCollector to collect hits against each
individual SegmentReader. All the other changes stem from this ;)
* Deprecates
** TopFieldDocCollector
** FieldSortedHitQueue
Okay, its not a handbook, but this should be a much better summary. Hopefully I
didnt miss anything too major.
> Change IndexSearcher multisegment searches to search each individual segment
> using a single HitCollector
> --------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-1483
> URL: https://issues.apache.org/jira/browse/LUCENE-1483
> Project: Lucene - Java
> Issue Type: Improvement
> Affects Versions: 2.9
> Reporter: Mark Miller
> Priority: Minor
> Attachments: LUCENE-1483-partial.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch, LUCENE-1483.patch,
> sortBench.py, sortCollate.py
>
>
> This issue changes how an IndexSearcher searches over multiple segments. The
> current method of searching multiple segments is to use a MultiSegmentReader
> and treat all of the segments as one. This causes filters and FieldCaches to
> be keyed to the MultiReader and makes reopen expensive. If only a few
> segments change, the FieldCache is still loaded for all of them.
> This patch changes things by searching each individual segment one at a time,
> but sharing the HitCollector used across each segment. This allows
> FieldCaches and Filters to be keyed on individual SegmentReaders, making
> reopen much cheaper. FieldCache loading over multiple segments can be much
> faster as well - with the old method, all unique terms for every segment is
> enumerated against each segment - because of the likely logarithmic change in
> terms per segment, this can be very wasteful. Searching individual segments
> avoids this cost. The term/document statistics from the multireader are used
> to score results for each segment.
> When sorting, its more difficult to use a single HitCollector for each sub
> searcher. Ordinals are not comparable across segments. To account for this, a
> new sort enabled HitCollector is introduced that is able to collect and sort
> across segments (because of its ability to compare ordinals across segments).
> This TopFieldCollector class will collect the values/ordinals for a given
> segment, and upon moving to the next segment, translate any ordinals/values
> so that they can be compared against the values for the new segment. This is
> done lazily.
> All and all, the switch seems to provide numerous performance benefits, in
> both sorted and non sorted search. We were seeing a good loss on indices with
> lots of segments (1000?) and certain queue sizes / queries, but the latest
> results seem to show thats been mostly taken care of (you shouldnt be using
> such a large queue on such a segmented index anyway).
> * Introduces
> ** MultiReaderHitCollector - a HitCollector that can collect across multiple
> IndexReaders. Old HitCollectors are wrapped to support multiple IndexReaders.
> ** TopFieldCollector - a HitCollector that can compare values/ordinals across
> IndexReaders and sort on fields.
> ** FieldValueHitQueue - a Priority queue that is part of the
> TopFieldCollector implementation.
> ** FieldComparator - a new Comparator class that works across IndexReaders.
> Part of the TopFieldCollector implementation.
> ** FieldComparatorSource - new class to allow for custom Comparators.
> * Alters
> ** IndexSearcher uses a single HitCollector to collect hits against each
> individual SegmentReader. All the other changes stem from this ;)
> * Deprecates
> ** TopFieldDocCollector
> ** FieldSortedHitQueue
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