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// Copyright (c) 2016 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
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an "AS
// express or implied. See the License for the specific language
// governing permissions and limitations under the License.
package cellar
// MergePolicy is anything which can prescribe a set of Merges to be done
type MergePolicy interface {
Merges(*Cellar, segmentList) []*Merge
// SimpleMergePolicy has no brain at all, it simply always chooses to merge
// two consecutive segments that are not already being merged
type SimpleMergePolicy struct{}
// Merges returns the set of prescribed merge operations for this set of segments
func (s *SimpleMergePolicy) Merges(cellar *Cellar, segments segmentList) []*Merge {
//rv := make([]*Merge, 0)
var rv []*Merge
consecutive := make(segmentList, 0)
for i := len(segments) - 1; i >= 0; i-- {
segment := segments[i]
if segment.mergeInProgress == 0 {
// insert, not append to keep the order the same (we're iterating reverse)
consecutive = append(consecutive, nil)
copy(consecutive[1:], consecutive[:])
consecutive[0] = segment
if len(consecutive) == 2 {
rv = append(rv, &Merge{
cellar: cellar,
sources: consecutive,
dropDeletes: (i == len(segments)-2), // if merging last 2 segments, we can drop deletes
consecutive = make(segmentList, 0)
} else {
// found a segment with merge in progress, so start over
consecutive = make(segmentList, 0)
return rv
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