diff options
Diffstat (limited to 'vendor/github.com/blevesearch/zap/v13/merge.go')
| -rw-r--r-- | vendor/github.com/blevesearch/zap/v13/merge.go | 847 |
1 files changed, 847 insertions, 0 deletions
diff --git a/vendor/github.com/blevesearch/zap/v13/merge.go b/vendor/github.com/blevesearch/zap/v13/merge.go new file mode 100644 index 0000000000..805100fb5f --- /dev/null +++ b/vendor/github.com/blevesearch/zap/v13/merge.go @@ -0,0 +1,847 @@ +// Copyright (c) 2017 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 zap + +import ( + "bufio" + "bytes" + "encoding/binary" + "fmt" + "math" + "os" + "sort" + + "github.com/RoaringBitmap/roaring" + seg "github.com/blevesearch/bleve/index/scorch/segment" + "github.com/couchbase/vellum" + "github.com/golang/snappy" +) + +var DefaultFileMergerBufferSize = 1024 * 1024 + +const docDropped = math.MaxUint64 // sentinel docNum to represent a deleted doc + +// Merge takes a slice of segments and bit masks describing which +// documents may be dropped, and creates a new segment containing the +// remaining data. This new segment is built at the specified path. +func (*ZapPlugin) Merge(segments []seg.Segment, drops []*roaring.Bitmap, path string, + closeCh chan struct{}, s seg.StatsReporter) ( + [][]uint64, uint64, error) { + + segmentBases := make([]*SegmentBase, len(segments)) + for segmenti, segment := range segments { + switch segmentx := segment.(type) { + case *Segment: + segmentBases[segmenti] = &segmentx.SegmentBase + case *SegmentBase: + segmentBases[segmenti] = segmentx + default: + panic(fmt.Sprintf("oops, unexpected segment type: %T", segment)) + } + } + return mergeSegmentBases(segmentBases, drops, path, DefaultChunkMode, closeCh, s) +} + +func mergeSegmentBases(segmentBases []*SegmentBase, drops []*roaring.Bitmap, path string, + chunkMode uint32, closeCh chan struct{}, s seg.StatsReporter) ( + [][]uint64, uint64, error) { + flag := os.O_RDWR | os.O_CREATE + + f, err := os.OpenFile(path, flag, 0600) + if err != nil { + return nil, 0, err + } + + cleanup := func() { + _ = f.Close() + _ = os.Remove(path) + } + + // buffer the output + br := bufio.NewWriterSize(f, DefaultFileMergerBufferSize) + + // wrap it for counting (tracking offsets) + cr := NewCountHashWriterWithStatsReporter(br, s) + + newDocNums, numDocs, storedIndexOffset, fieldsIndexOffset, docValueOffset, _, _, _, err := + MergeToWriter(segmentBases, drops, chunkMode, cr, closeCh) + if err != nil { + cleanup() + return nil, 0, err + } + + err = persistFooter(numDocs, storedIndexOffset, fieldsIndexOffset, + docValueOffset, chunkMode, cr.Sum32(), cr) + if err != nil { + cleanup() + return nil, 0, err + } + + err = br.Flush() + if err != nil { + cleanup() + return nil, 0, err + } + + err = f.Sync() + if err != nil { + cleanup() + return nil, 0, err + } + + err = f.Close() + if err != nil { + cleanup() + return nil, 0, err + } + + return newDocNums, uint64(cr.Count()), nil +} + +func MergeToWriter(segments []*SegmentBase, drops []*roaring.Bitmap, + chunkMode uint32, cr *CountHashWriter, closeCh chan struct{}) ( + newDocNums [][]uint64, + numDocs, storedIndexOffset, fieldsIndexOffset, docValueOffset uint64, + dictLocs []uint64, fieldsInv []string, fieldsMap map[string]uint16, + err error) { + docValueOffset = uint64(fieldNotUninverted) + + var fieldsSame bool + fieldsSame, fieldsInv = mergeFields(segments) + fieldsMap = mapFields(fieldsInv) + + numDocs = computeNewDocCount(segments, drops) + + if isClosed(closeCh) { + return nil, 0, 0, 0, 0, nil, nil, nil, seg.ErrClosed + } + + if numDocs > 0 { + storedIndexOffset, newDocNums, err = mergeStoredAndRemap(segments, drops, + fieldsMap, fieldsInv, fieldsSame, numDocs, cr, closeCh) + if err != nil { + return nil, 0, 0, 0, 0, nil, nil, nil, err + } + + dictLocs, docValueOffset, err = persistMergedRest(segments, drops, + fieldsInv, fieldsMap, fieldsSame, + newDocNums, numDocs, chunkMode, cr, closeCh) + if err != nil { + return nil, 0, 0, 0, 0, nil, nil, nil, err + } + } else { + dictLocs = make([]uint64, len(fieldsInv)) + } + + fieldsIndexOffset, err = persistFields(fieldsInv, cr, dictLocs) + if err != nil { + return nil, 0, 0, 0, 0, nil, nil, nil, err + } + + return newDocNums, numDocs, storedIndexOffset, fieldsIndexOffset, docValueOffset, dictLocs, fieldsInv, fieldsMap, nil +} + +// mapFields takes the fieldsInv list and returns a map of fieldName +// to fieldID+1 +func mapFields(fields []string) map[string]uint16 { + rv := make(map[string]uint16, len(fields)) + for i, fieldName := range fields { + rv[fieldName] = uint16(i) + 1 + } + return rv +} + +// computeNewDocCount determines how many documents will be in the newly +// merged segment when obsoleted docs are dropped +func computeNewDocCount(segments []*SegmentBase, drops []*roaring.Bitmap) uint64 { + var newDocCount uint64 + for segI, segment := range segments { + newDocCount += segment.numDocs + if drops[segI] != nil { + newDocCount -= drops[segI].GetCardinality() + } + } + return newDocCount +} + +func persistMergedRest(segments []*SegmentBase, dropsIn []*roaring.Bitmap, + fieldsInv []string, fieldsMap map[string]uint16, fieldsSame bool, + newDocNumsIn [][]uint64, newSegDocCount uint64, chunkMode uint32, + w *CountHashWriter, closeCh chan struct{}) ([]uint64, uint64, error) { + + var bufMaxVarintLen64 []byte = make([]byte, binary.MaxVarintLen64) + var bufLoc []uint64 + + var postings *PostingsList + var postItr *PostingsIterator + + rv := make([]uint64, len(fieldsInv)) + fieldDvLocsStart := make([]uint64, len(fieldsInv)) + fieldDvLocsEnd := make([]uint64, len(fieldsInv)) + + // these int coders are initialized with chunk size 1024 + // however this will be reset to the correct chunk size + // while processing each individual field-term section + tfEncoder := newChunkedIntCoder(1024, newSegDocCount-1) + locEncoder := newChunkedIntCoder(1024, newSegDocCount-1) + + var vellumBuf bytes.Buffer + newVellum, err := vellum.New(&vellumBuf, nil) + if err != nil { + return nil, 0, err + } + + newRoaring := roaring.NewBitmap() + + // for each field + for fieldID, fieldName := range fieldsInv { + + // collect FST iterators from all active segments for this field + var newDocNums [][]uint64 + var drops []*roaring.Bitmap + var dicts []*Dictionary + var itrs []vellum.Iterator + + var segmentsInFocus []*SegmentBase + + for segmentI, segment := range segments { + + // check for the closure in meantime + if isClosed(closeCh) { + return nil, 0, seg.ErrClosed + } + + dict, err2 := segment.dictionary(fieldName) + if err2 != nil { + return nil, 0, err2 + } + if dict != nil && dict.fst != nil { + itr, err2 := dict.fst.Iterator(nil, nil) + if err2 != nil && err2 != vellum.ErrIteratorDone { + return nil, 0, err2 + } + if itr != nil { + newDocNums = append(newDocNums, newDocNumsIn[segmentI]) + if dropsIn[segmentI] != nil && !dropsIn[segmentI].IsEmpty() { + drops = append(drops, dropsIn[segmentI]) + } else { + drops = append(drops, nil) + } + dicts = append(dicts, dict) + itrs = append(itrs, itr) + segmentsInFocus = append(segmentsInFocus, segment) + } + } + } + + var prevTerm []byte + + newRoaring.Clear() + + var lastDocNum, lastFreq, lastNorm uint64 + + // determines whether to use "1-hit" encoding optimization + // when a term appears in only 1 doc, with no loc info, + // has freq of 1, and the docNum fits into 31-bits + use1HitEncoding := func(termCardinality uint64) (bool, uint64, uint64) { + if termCardinality == uint64(1) && locEncoder.FinalSize() <= 0 { + docNum := uint64(newRoaring.Minimum()) + if under32Bits(docNum) && docNum == lastDocNum && lastFreq == 1 { + return true, docNum, lastNorm + } + } + return false, 0, 0 + } + + finishTerm := func(term []byte) error { + tfEncoder.Close() + locEncoder.Close() + + postingsOffset, err := writePostings(newRoaring, + tfEncoder, locEncoder, use1HitEncoding, w, bufMaxVarintLen64) + if err != nil { + return err + } + + if postingsOffset > 0 { + err = newVellum.Insert(term, postingsOffset) + if err != nil { + return err + } + } + + newRoaring.Clear() + + tfEncoder.Reset() + locEncoder.Reset() + + lastDocNum = 0 + lastFreq = 0 + lastNorm = 0 + + return nil + } + + enumerator, err := newEnumerator(itrs) + + for err == nil { + term, itrI, postingsOffset := enumerator.Current() + + if !bytes.Equal(prevTerm, term) { + // check for the closure in meantime + if isClosed(closeCh) { + return nil, 0, seg.ErrClosed + } + + // if the term changed, write out the info collected + // for the previous term + err = finishTerm(prevTerm) + if err != nil { + return nil, 0, err + } + } + if !bytes.Equal(prevTerm, term) || prevTerm == nil { + // compute cardinality of field-term in new seg + var newCard uint64 + lowItrIdxs, lowItrVals := enumerator.GetLowIdxsAndValues() + for i, idx := range lowItrIdxs { + pl, err := dicts[idx].postingsListFromOffset(lowItrVals[i], drops[idx], nil) + if err != nil { + return nil, 0, err + } + newCard += pl.Count() + } + // compute correct chunk size with this + chunkSize, err := getChunkSize(chunkMode, newCard, newSegDocCount) + if err != nil { + return nil, 0, err + } + // update encoders chunk + tfEncoder.SetChunkSize(chunkSize, newSegDocCount-1) + locEncoder.SetChunkSize(chunkSize, newSegDocCount-1) + } + + postings, err = dicts[itrI].postingsListFromOffset( + postingsOffset, drops[itrI], postings) + if err != nil { + return nil, 0, err + } + + postItr = postings.iterator(true, true, true, postItr) + + // can no longer optimize by copying, since chunk factor could have changed + lastDocNum, lastFreq, lastNorm, bufLoc, err = mergeTermFreqNormLocs( + fieldsMap, term, postItr, newDocNums[itrI], newRoaring, + tfEncoder, locEncoder, bufLoc) + + if err != nil { + return nil, 0, err + } + + prevTerm = prevTerm[:0] // copy to prevTerm in case Next() reuses term mem + prevTerm = append(prevTerm, term...) + + err = enumerator.Next() + } + if err != vellum.ErrIteratorDone { + return nil, 0, err + } + + err = finishTerm(prevTerm) + if err != nil { + return nil, 0, err + } + + dictOffset := uint64(w.Count()) + + err = newVellum.Close() + if err != nil { + return nil, 0, err + } + vellumData := vellumBuf.Bytes() + + // write out the length of the vellum data + n := binary.PutUvarint(bufMaxVarintLen64, uint64(len(vellumData))) + _, err = w.Write(bufMaxVarintLen64[:n]) + if err != nil { + return nil, 0, err + } + + // write this vellum to disk + _, err = w.Write(vellumData) + if err != nil { + return nil, 0, err + } + + rv[fieldID] = dictOffset + + // get the field doc value offset (start) + fieldDvLocsStart[fieldID] = uint64(w.Count()) + + // update the field doc values + // NOTE: doc values continue to use legacy chunk mode + chunkSize, err := getChunkSize(LegacyChunkMode, 0, 0) + if err != nil { + return nil, 0, err + } + fdvEncoder := newChunkedContentCoder(chunkSize, newSegDocCount-1, w, true) + + fdvReadersAvailable := false + var dvIterClone *docValueReader + for segmentI, segment := range segmentsInFocus { + // check for the closure in meantime + if isClosed(closeCh) { + return nil, 0, seg.ErrClosed + } + + fieldIDPlus1 := uint16(segment.fieldsMap[fieldName]) + if dvIter, exists := segment.fieldDvReaders[fieldIDPlus1-1]; exists && + dvIter != nil { + fdvReadersAvailable = true + dvIterClone = dvIter.cloneInto(dvIterClone) + err = dvIterClone.iterateAllDocValues(segment, func(docNum uint64, terms []byte) error { + if newDocNums[segmentI][docNum] == docDropped { + return nil + } + err := fdvEncoder.Add(newDocNums[segmentI][docNum], terms) + if err != nil { + return err + } + return nil + }) + if err != nil { + return nil, 0, err + } + } + } + + if fdvReadersAvailable { + err = fdvEncoder.Close() + if err != nil { + return nil, 0, err + } + + // persist the doc value details for this field + _, err = fdvEncoder.Write() + if err != nil { + return nil, 0, err + } + + // get the field doc value offset (end) + fieldDvLocsEnd[fieldID] = uint64(w.Count()) + } else { + fieldDvLocsStart[fieldID] = fieldNotUninverted + fieldDvLocsEnd[fieldID] = fieldNotUninverted + } + + // reset vellum buffer and vellum builder + vellumBuf.Reset() + err = newVellum.Reset(&vellumBuf) + if err != nil { + return nil, 0, err + } + } + + fieldDvLocsOffset := uint64(w.Count()) + + buf := bufMaxVarintLen64 + for i := 0; i < len(fieldDvLocsStart); i++ { + n := binary.PutUvarint(buf, fieldDvLocsStart[i]) + _, err := w.Write(buf[:n]) + if err != nil { + return nil, 0, err + } + n = binary.PutUvarint(buf, fieldDvLocsEnd[i]) + _, err = w.Write(buf[:n]) + if err != nil { + return nil, 0, err + } + } + + return rv, fieldDvLocsOffset, nil +} + +func mergeTermFreqNormLocs(fieldsMap map[string]uint16, term []byte, postItr *PostingsIterator, + newDocNums []uint64, newRoaring *roaring.Bitmap, + tfEncoder *chunkedIntCoder, locEncoder *chunkedIntCoder, bufLoc []uint64) ( + lastDocNum uint64, lastFreq uint64, lastNorm uint64, bufLocOut []uint64, err error) { + next, err := postItr.Next() + for next != nil && err == nil { + hitNewDocNum := newDocNums[next.Number()] + if hitNewDocNum == docDropped { + return 0, 0, 0, nil, fmt.Errorf("see hit with dropped docNum") + } + + newRoaring.Add(uint32(hitNewDocNum)) + + nextFreq := next.Frequency() + nextNorm := uint64(math.Float32bits(float32(next.Norm()))) + + locs := next.Locations() + + err = tfEncoder.Add(hitNewDocNum, + encodeFreqHasLocs(nextFreq, len(locs) > 0), nextNorm) + if err != nil { + return 0, 0, 0, nil, err + } + + if len(locs) > 0 { + numBytesLocs := 0 + for _, loc := range locs { + ap := loc.ArrayPositions() + numBytesLocs += totalUvarintBytes(uint64(fieldsMap[loc.Field()]-1), + loc.Pos(), loc.Start(), loc.End(), uint64(len(ap)), ap) + } + + err = locEncoder.Add(hitNewDocNum, uint64(numBytesLocs)) + if err != nil { + return 0, 0, 0, nil, err + } + + for _, loc := range locs { + ap := loc.ArrayPositions() + if cap(bufLoc) < 5+len(ap) { + bufLoc = make([]uint64, 0, 5+len(ap)) + } + args := bufLoc[0:5] + args[0] = uint64(fieldsMap[loc.Field()] - 1) + args[1] = loc.Pos() + args[2] = loc.Start() + args[3] = loc.End() + args[4] = uint64(len(ap)) + args = append(args, ap...) + err = locEncoder.Add(hitNewDocNum, args...) + if err != nil { + return 0, 0, 0, nil, err + } + } + } + + lastDocNum = hitNewDocNum + lastFreq = nextFreq + lastNorm = nextNorm + + next, err = postItr.Next() + } + + return lastDocNum, lastFreq, lastNorm, bufLoc, err +} + +func writePostings(postings *roaring.Bitmap, tfEncoder, locEncoder *chunkedIntCoder, + use1HitEncoding func(uint64) (bool, uint64, uint64), + w *CountHashWriter, bufMaxVarintLen64 []byte) ( + offset uint64, err error) { + termCardinality := postings.GetCardinality() + if termCardinality <= 0 { + return 0, nil + } + + if use1HitEncoding != nil { + encodeAs1Hit, docNum1Hit, normBits1Hit := use1HitEncoding(termCardinality) + if encodeAs1Hit { + return FSTValEncode1Hit(docNum1Hit, normBits1Hit), nil + } + } + + var tfOffset uint64 + tfOffset, _, err = tfEncoder.writeAt(w) + if err != nil { + return 0, err + } + + var locOffset uint64 + locOffset, _, err = locEncoder.writeAt(w) + if err != nil { + return 0, err + } + + postingsOffset := uint64(w.Count()) + + n := binary.PutUvarint(bufMaxVarintLen64, tfOffset) + _, err = w.Write(bufMaxVarintLen64[:n]) + if err != nil { + return 0, err + } + + n = binary.PutUvarint(bufMaxVarintLen64, locOffset) + _, err = w.Write(bufMaxVarintLen64[:n]) + if err != nil { + return 0, err + } + + _, err = writeRoaringWithLen(postings, w, bufMaxVarintLen64) + if err != nil { + return 0, err + } + + return postingsOffset, nil +} + +type varintEncoder func(uint64) (int, error) + +func mergeStoredAndRemap(segments []*SegmentBase, drops []*roaring.Bitmap, + fieldsMap map[string]uint16, fieldsInv []string, fieldsSame bool, newSegDocCount uint64, + w *CountHashWriter, closeCh chan struct{}) (uint64, [][]uint64, error) { + var rv [][]uint64 // The remapped or newDocNums for each segment. + + var newDocNum uint64 + + var curr int + var data, compressed []byte + var metaBuf bytes.Buffer + varBuf := make([]byte, binary.MaxVarintLen64) + metaEncode := func(val uint64) (int, error) { + wb := binary.PutUvarint(varBuf, val) + return metaBuf.Write(varBuf[:wb]) + } + + vals := make([][][]byte, len(fieldsInv)) + typs := make([][]byte, len(fieldsInv)) + poss := make([][][]uint64, len(fieldsInv)) + + var posBuf []uint64 + + docNumOffsets := make([]uint64, newSegDocCount) + + vdc := visitDocumentCtxPool.Get().(*visitDocumentCtx) + defer visitDocumentCtxPool.Put(vdc) + + // for each segment + for segI, segment := range segments { + // check for the closure in meantime + if isClosed(closeCh) { + return 0, nil, seg.ErrClosed + } + + segNewDocNums := make([]uint64, segment.numDocs) + + dropsI := drops[segI] + + // optimize when the field mapping is the same across all + // segments and there are no deletions, via byte-copying + // of stored docs bytes directly to the writer + if fieldsSame && (dropsI == nil || dropsI.GetCardinality() == 0) { + err := segment.copyStoredDocs(newDocNum, docNumOffsets, w) + if err != nil { + return 0, nil, err + } + + for i := uint64(0); i < segment.numDocs; i++ { + segNewDocNums[i] = newDocNum + newDocNum++ + } + rv = append(rv, segNewDocNums) + + continue + } + + // for each doc num + for docNum := uint64(0); docNum < segment.numDocs; docNum++ { + // TODO: roaring's API limits docNums to 32-bits? + if dropsI != nil && dropsI.Contains(uint32(docNum)) { + segNewDocNums[docNum] = docDropped + continue + } + + segNewDocNums[docNum] = newDocNum + + curr = 0 + metaBuf.Reset() + data = data[:0] + + posTemp := posBuf + + // collect all the data + for i := 0; i < len(fieldsInv); i++ { + vals[i] = vals[i][:0] + typs[i] = typs[i][:0] + poss[i] = poss[i][:0] + } + err := segment.visitDocument(vdc, docNum, func(field string, typ byte, value []byte, pos []uint64) bool { + fieldID := int(fieldsMap[field]) - 1 + vals[fieldID] = append(vals[fieldID], value) + typs[fieldID] = append(typs[fieldID], typ) + + // copy array positions to preserve them beyond the scope of this callback + var curPos []uint64 + if len(pos) > 0 { + if cap(posTemp) < len(pos) { + posBuf = make([]uint64, len(pos)*len(fieldsInv)) + posTemp = posBuf + } + curPos = posTemp[0:len(pos)] + copy(curPos, pos) + posTemp = posTemp[len(pos):] + } + poss[fieldID] = append(poss[fieldID], curPos) + + return true + }) + if err != nil { + return 0, nil, err + } + + // _id field special case optimizes ExternalID() lookups + idFieldVal := vals[uint16(0)][0] + _, err = metaEncode(uint64(len(idFieldVal))) + if err != nil { + return 0, nil, err + } + + // now walk the non-"_id" fields in order + for fieldID := 1; fieldID < len(fieldsInv); fieldID++ { + storedFieldValues := vals[fieldID] + + stf := typs[fieldID] + spf := poss[fieldID] + + var err2 error + curr, data, err2 = persistStoredFieldValues(fieldID, + storedFieldValues, stf, spf, curr, metaEncode, data) + if err2 != nil { + return 0, nil, err2 + } + } + + metaBytes := metaBuf.Bytes() + + compressed = snappy.Encode(compressed[:cap(compressed)], data) + + // record where we're about to start writing + docNumOffsets[newDocNum] = uint64(w.Count()) + + // write out the meta len and compressed data len + _, err = writeUvarints(w, + uint64(len(metaBytes)), + uint64(len(idFieldVal)+len(compressed))) + if err != nil { + return 0, nil, err + } + // now write the meta + _, err = w.Write(metaBytes) + if err != nil { + return 0, nil, err + } + // now write the _id field val (counted as part of the 'compressed' data) + _, err = w.Write(idFieldVal) + if err != nil { + return 0, nil, err + } + // now write the compressed data + _, err = w.Write(compressed) + if err != nil { + return 0, nil, err + } + + newDocNum++ + } + + rv = append(rv, segNewDocNums) + } + + // return value is the start of the stored index + storedIndexOffset := uint64(w.Count()) + + // now write out the stored doc index + for _, docNumOffset := range docNumOffsets { + err := binary.Write(w, binary.BigEndian, docNumOffset) + if err != nil { + return 0, nil, err + } + } + + return storedIndexOffset, rv, nil +} + +// copyStoredDocs writes out a segment's stored doc info, optimized by +// using a single Write() call for the entire set of bytes. The +// newDocNumOffsets is filled with the new offsets for each doc. +func (s *SegmentBase) copyStoredDocs(newDocNum uint64, newDocNumOffsets []uint64, + w *CountHashWriter) error { + if s.numDocs <= 0 { + return nil + } + + indexOffset0, storedOffset0, _, _, _ := + s.getDocStoredOffsets(0) // the segment's first doc + + indexOffsetN, storedOffsetN, readN, metaLenN, dataLenN := + s.getDocStoredOffsets(s.numDocs - 1) // the segment's last doc + + storedOffset0New := uint64(w.Count()) + + storedBytes := s.mem[storedOffset0 : storedOffsetN+readN+metaLenN+dataLenN] + _, err := w.Write(storedBytes) + if err != nil { + return err + } + + // remap the storedOffset's for the docs into new offsets relative + // to storedOffset0New, filling the given docNumOffsetsOut array + for indexOffset := indexOffset0; indexOffset <= indexOffsetN; indexOffset += 8 { + storedOffset := binary.BigEndian.Uint64(s.mem[indexOffset : indexOffset+8]) + storedOffsetNew := storedOffset - storedOffset0 + storedOffset0New + newDocNumOffsets[newDocNum] = storedOffsetNew + newDocNum += 1 + } + + return nil +} + +// mergeFields builds a unified list of fields used across all the +// input segments, and computes whether the fields are the same across +// segments (which depends on fields to be sorted in the same way +// across segments) +func mergeFields(segments []*SegmentBase) (bool, []string) { + fieldsSame := true + + var segment0Fields []string + if len(segments) > 0 { + segment0Fields = segments[0].Fields() + } + + fieldsExist := map[string]struct{}{} + for _, segment := range segments { + fields := segment.Fields() + for fieldi, field := range fields { + fieldsExist[field] = struct{}{} + if len(segment0Fields) != len(fields) || segment0Fields[fieldi] != field { + fieldsSame = false + } + } + } + + rv := make([]string, 0, len(fieldsExist)) + // ensure _id stays first + rv = append(rv, "_id") + for k := range fieldsExist { + if k != "_id" { + rv = append(rv, k) + } + } + + sort.Strings(rv[1:]) // leave _id as first + + return fieldsSame, rv +} + +func isClosed(closeCh chan struct{}) bool { + select { + case <-closeCh: + return true + default: + return false + } +} |