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batch.go
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batch.go
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// Copyright 2017-2019 Lei Ni (nilei81@gmail.com)
//
// 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 logdb
import (
pb "github.com/lni/dragonboat/raftpb"
)
//
// Rather than storing each raft entry as an individual record, dragonboat
// batches entries first, each persisted record can thus contain many raft
// entries. This idea is based on the observations that:
// * entries are usually saved together
// * entries are usually read and consumed together
// This idea helped to achieve better latency and throughput performance.
//
// We also compact redundent index/term values whenever possible. In such
// approach, rather than repeatedly storing the continously increamental
// index values and the identifical term values, we represent them in the
// way implemented in the compactBatchFields function below.
//
// To the maximum of our knowledge, dragonboat is the original inventor
// of the ideas above, they were publicly disclosed on github.com when
// dragnoboat made its first public release.
//
// To use/implement the above ideas in your software, please include the
// above copyright notice in your source file, dragonboat's Apache2 license
// also requires to include dragonboat's NOTICE file.
//
func getBatchID(index uint64) uint64 {
return index / batchSize
}
func entriesSize(ents []pb.Entry) uint64 {
sz := uint64(0)
for _, e := range ents {
sz += uint64(e.SizeUpperLimit())
}
return sz
}
func getBatchIDRange(low uint64, high uint64) (uint64, uint64) {
lowBatchID := getBatchID(low)
highBatchID := getBatchID(high)
if high%batchSize == 0 {
return lowBatchID, highBatchID
}
return lowBatchID, highBatchID + 1
}
func restoreBatchFields(eb pb.EntryBatch) pb.EntryBatch {
if len(eb.Entries) <= 1 {
panic("restore called on small batch")
}
if eb.Entries[len(eb.Entries)-1].Term == 0 {
term := eb.Entries[0].Term
idx := eb.Entries[0].Index
for i := 1; i < len(eb.Entries); i++ {
eb.Entries[i].Term = term
eb.Entries[i].Index = idx + uint64(i)
}
}
return eb
}
func compactBatchFields(eb pb.EntryBatch) pb.EntryBatch {
if len(eb.Entries) <= 1 {
panic("compact called on small batch")
}
expLastIdx := eb.Entries[0].Index + uint64(len(eb.Entries)-1)
if eb.Entries[0].Term == eb.Entries[len(eb.Entries)-1].Term &&
expLastIdx == eb.Entries[len(eb.Entries)-1].Index {
for i := 1; i < len(eb.Entries); i++ {
eb.Entries[i].Term = 0
eb.Entries[i].Index = 0
}
}
return eb
}
func getMergedFirstBatch(eb pb.EntryBatch, lb pb.EntryBatch) pb.EntryBatch {
if len(eb.Entries) == 0 || len(lb.Entries) == 0 {
panic("getMergedFirstBatch called on empty batch")
}
batchID := getBatchID(eb.Entries[0].Index)
if batchID < getBatchID(lb.Entries[0].Index) {
panic("eb batch < lb batch")
}
if batchID > getBatchID(lb.Entries[0].Index) {
return eb
}
if eb.Entries[0].Index > lb.Entries[0].Index {
if eb.Entries[0].Index <= lb.Entries[len(lb.Entries)-1].Index {
firstIndex := eb.Entries[0].Index
i := 0
for ; i < len(lb.Entries); i++ {
if lb.Entries[i].Index >= firstIndex {
break
}
}
lb.Entries = append(lb.Entries[:i], eb.Entries...)
} else {
lb.Entries = append(lb.Entries, eb.Entries...)
}
return lb
}
return eb
}