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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 store
// At the moment this happens to be the same interface as described by
// RocksDB, but this may not always be the case.
type MergeOperator interface {
// FullMerge the full sequence of operands on top of the existingValue
// if no value currently exists, existingValue is nil
// return the merged value, and success/failure
FullMerge(key, existingValue []byte, operands [][]byte) ([]byte, bool)
// Partially merge these two operands.
// If partial merge cannot be done, return nil,false, which will defer
// all processing until the FullMerge is done.
PartialMerge(key, leftOperand, rightOperand []byte) ([]byte, bool)
// Name returns an identifier for the operator
Name() string
}
type EmulatedMerge struct {
Merges map[string][][]byte
mo MergeOperator
}
func NewEmulatedMerge(mo MergeOperator) *EmulatedMerge {
return &EmulatedMerge{
Merges: make(map[string][][]byte),
mo: mo,
}
}
func (m *EmulatedMerge) Merge(key, val []byte) {
ops, ok := m.Merges[string(key)]
if ok && len(ops) > 0 {
last := ops[len(ops)-1]
mergedVal, partialMergeOk := m.mo.PartialMerge(key, last, val)
if partialMergeOk {
// replace last entry with the result of the merge
ops[len(ops)-1] = mergedVal
} else {
// could not partial merge, append this to the end
ops = append(ops, val)
}
} else {
ops = [][]byte{val}
}
m.Merges[string(key)] = ops
}
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