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topn.go
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topn.go
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// Copyright (c) 2014 Couchbase, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package collector
import (
"time"
"github.com/blevesearch/bleve/index"
"github.com/blevesearch/bleve/search"
"golang.org/x/net/context"
)
type collectorStore interface {
// Add the document, and if the new store size exceeds the provided size
// the last element is removed and returned. If the size has not been
// exceeded, nil is returned.
AddNotExceedingSize(doc *search.DocumentMatch, size int) *search.DocumentMatch
Final(skip int, fixup collectorFixup) (search.DocumentMatchCollection, error)
}
// PreAllocSizeSkipCap will cap preallocation to this amount when
// size+skip exceeds this value
var PreAllocSizeSkipCap = 1000
type collectorCompare func(i, j *search.DocumentMatch) int
type collectorFixup func(d *search.DocumentMatch) error
// TopNCollector collects the top N hits, optionally skipping some results
type TopNCollector struct {
size int
skip int
total uint64
maxScore float64
took time.Duration
sort search.SortOrder
results search.DocumentMatchCollection
facetsBuilder *search.FacetsBuilder
store collectorStore
needDocIds bool
neededFields []string
cachedScoring []bool
cachedDesc []bool
lowestMatchOutsideResults *search.DocumentMatch
}
// CheckDoneEvery controls how frequently we check the context deadline
const CheckDoneEvery = uint64(1024)
// NewTopNCollector builds a collector to find the top 'size' hits
// skipping over the first 'skip' hits
// ordering hits by the provided sort order
func NewTopNCollector(size int, skip int, sort search.SortOrder) *TopNCollector {
hc := &TopNCollector{size: size, skip: skip, sort: sort}
// pre-allocate space on the store to avoid reslicing
// unless the size + skip is too large, then cap it
// everything should still work, just reslices as necessary
backingSize := size + skip + 1
if size+skip > PreAllocSizeSkipCap {
backingSize = PreAllocSizeSkipCap + 1
}
if size+skip > 10 {
hc.store = newStoreHeap(backingSize, func(i, j *search.DocumentMatch) int {
return hc.sort.Compare(hc.cachedScoring, hc.cachedDesc, i, j)
})
} else {
hc.store = newStoreSlice(backingSize, func(i, j *search.DocumentMatch) int {
return hc.sort.Compare(hc.cachedScoring, hc.cachedDesc, i, j)
})
}
// these lookups traverse an interface, so do once up-front
if sort.RequiresDocID() {
hc.needDocIds = true
}
hc.neededFields = sort.RequiredFields()
hc.cachedScoring = sort.CacheIsScore()
hc.cachedDesc = sort.CacheDescending()
return hc
}
// Collect goes to the index to find the matching documents
func (hc *TopNCollector) Collect(ctx context.Context, searcher search.Searcher, reader index.IndexReader) error {
startTime := time.Now()
var err error
var next *search.DocumentMatch
// pre-allocate enough space in the DocumentMatchPool
// unless the size + skip is too large, then cap it
// everything should still work, just allocates DocumentMatches on demand
backingSize := hc.size + hc.skip + 1
if hc.size+hc.skip > PreAllocSizeSkipCap {
backingSize = PreAllocSizeSkipCap + 1
}
searchContext := &search.SearchContext{
DocumentMatchPool: search.NewDocumentMatchPool(backingSize+searcher.DocumentMatchPoolSize(), len(hc.sort)),
}
select {
case <-ctx.Done():
return ctx.Err()
default:
next, err = searcher.Next(searchContext)
}
for err == nil && next != nil {
if hc.total%CheckDoneEvery == 0 {
select {
case <-ctx.Done():
return ctx.Err()
default:
}
}
err = hc.collectSingle(searchContext, reader, next)
if err != nil {
break
}
next, err = searcher.Next(searchContext)
}
// compute search duration
hc.took = time.Since(startTime)
if err != nil {
return err
}
// finalize actual results
err = hc.finalizeResults(reader)
if err != nil {
return err
}
return nil
}
var sortByScoreOpt = []string{"_score"}
func (hc *TopNCollector) collectSingle(ctx *search.SearchContext, reader index.IndexReader, d *search.DocumentMatch) error {
var err error
// visit field terms for features that require it (sort, facets)
if len(hc.neededFields) > 0 {
err = hc.visitFieldTerms(reader, d)
if err != nil {
return err
}
}
// increment total hits
hc.total++
d.HitNumber = hc.total
// update max score
if d.Score > hc.maxScore {
hc.maxScore = d.Score
}
// see if we need to load ID (at this early stage, for example to sort on it)
if hc.needDocIds {
d.ID, err = reader.ExternalID(d.IndexInternalID)
if err != nil {
return err
}
}
// compute this hits sort value
if len(hc.sort) == 1 && hc.cachedScoring[0] {
d.Sort = sortByScoreOpt
} else {
hc.sort.Value(d)
}
// optimization, we track lowest sorting hit already removed from heap
// with this one comparison, we can avoid all heap operations if
// this hit would have been added and then immediately removed
if hc.lowestMatchOutsideResults != nil {
cmp := hc.sort.Compare(hc.cachedScoring, hc.cachedDesc, d, hc.lowestMatchOutsideResults)
if cmp >= 0 {
// this hit can't possibly be in the result set, so avoid heap ops
ctx.DocumentMatchPool.Put(d)
return nil
}
}
removed := hc.store.AddNotExceedingSize(d, hc.size+hc.skip)
if removed != nil {
if hc.lowestMatchOutsideResults == nil {
hc.lowestMatchOutsideResults = removed
} else {
cmp := hc.sort.Compare(hc.cachedScoring, hc.cachedDesc, removed, hc.lowestMatchOutsideResults)
if cmp < 0 {
tmp := hc.lowestMatchOutsideResults
hc.lowestMatchOutsideResults = removed
ctx.DocumentMatchPool.Put(tmp)
}
}
}
return nil
}
// visitFieldTerms is responsible for visiting the field terms of the
// search hit, and passing visited terms to the sort and facet builder
func (hc *TopNCollector) visitFieldTerms(reader index.IndexReader, d *search.DocumentMatch) error {
if hc.facetsBuilder != nil {
hc.facetsBuilder.StartDoc()
}
err := reader.DocumentVisitFieldTerms(d.IndexInternalID, hc.neededFields, func(field string, term []byte) {
if hc.facetsBuilder != nil {
hc.facetsBuilder.UpdateVisitor(field, term)
}
hc.sort.UpdateVisitor(field, term)
})
if hc.facetsBuilder != nil {
hc.facetsBuilder.EndDoc()
}
return err
}
// SetFacetsBuilder registers a facet builder for this collector
func (hc *TopNCollector) SetFacetsBuilder(facetsBuilder *search.FacetsBuilder) {
hc.facetsBuilder = facetsBuilder
hc.neededFields = append(hc.neededFields, hc.facetsBuilder.RequiredFields()...)
}
// finalizeResults starts with the heap containing the final top size+skip
// it now throws away the results to be skipped
// and does final doc id lookup (if necessary)
func (hc *TopNCollector) finalizeResults(r index.IndexReader) error {
var err error
hc.results, err = hc.store.Final(hc.skip, func(doc *search.DocumentMatch) error {
if doc.ID == "" {
// look up the id since we need it for lookup
var err error
doc.ID, err = r.ExternalID(doc.IndexInternalID)
if err != nil {
return err
}
}
return nil
})
return err
}
// Results returns the collected hits
func (hc *TopNCollector) Results() search.DocumentMatchCollection {
return hc.results
}
// Total returns the total number of hits
func (hc *TopNCollector) Total() uint64 {
return hc.total
}
// MaxScore returns the maximum score seen across all the hits
func (hc *TopNCollector) MaxScore() float64 {
return hc.maxScore
}
// Took returns the time spent collecting hits
func (hc *TopNCollector) Took() time.Duration {
return hc.took
}
// FacetResults returns the computed facets results
func (hc *TopNCollector) FacetResults() search.FacetResults {
if hc.facetsBuilder != nil {
return hc.facetsBuilder.Results()
}
return search.FacetResults{}
}