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// Copyright 2015 PingCAP, 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package kv
import (
"github.com/juju/errors"
)
var (
// DefaultTxnMembufCap is the default transaction membuf capability.
DefaultTxnMembufCap = 4 * 1024
// ImportingTxnMembufCap is the capability of tidb importing data situation.
ImportingTxnMembufCap = 32 * 1024
// TempTxnMemBufCap is the capability of temporary membuf.
TempTxnMemBufCap = 64
)
// BufferStore wraps a Retriever for read and a MemBuffer for buffered write.
// Common usage pattern:
// bs := NewBufferStore(r) // use BufferStore to wrap a Retriever
// // ...
// // read/write on bs
// // ...
// bs.SaveTo(m) // save above operations to a Mutator
type BufferStore struct {
MemBuffer
r Retriever
}
// NewBufferStore creates a BufferStore using r for read.
func NewBufferStore(r Retriever, cap int) *BufferStore {
if cap <= 0 {
cap = DefaultTxnMembufCap
}
return &BufferStore{
r: r,
MemBuffer: &lazyMemBuffer{cap: cap},
}
}
// Reset resets s.MemBuffer.
func (s *BufferStore) Reset() {
s.MemBuffer.Reset()
}
// SetCap sets the MemBuffer capability.
func (s *BufferStore) SetCap(cap int) {
s.MemBuffer.SetCap(cap)
}
// Get implements the Retriever interface.
func (s *BufferStore) Get(k Key) ([]byte, error) {
val, err := s.MemBuffer.Get(k)
if IsErrNotFound(err) {
val, err = s.r.Get(k)
}
if err != nil {
return nil, errors.Trace(err)
}
if len(val) == 0 {
return nil, ErrNotExist
}
return val, nil
}
// Iter implements the Retriever interface.
func (s *BufferStore) Iter(k Key, upperBound Key) (Iterator, error) {
bufferIt, err := s.MemBuffer.Iter(k, upperBound)
if err != nil {
return nil, errors.Trace(err)
}
retrieverIt, err := s.r.Iter(k, upperBound)
if err != nil {
return nil, errors.Trace(err)
}
return NewUnionIter(bufferIt, retrieverIt, false)
}
// IterReverse implements the Retriever interface.
func (s *BufferStore) IterReverse(k Key) (Iterator, error) {
bufferIt, err := s.MemBuffer.IterReverse(k)
if err != nil {
return nil, errors.Trace(err)
}
retrieverIt, err := s.r.IterReverse(k)
if err != nil {
return nil, errors.Trace(err)
}
return NewUnionIter(bufferIt, retrieverIt, true)
}
// WalkBuffer iterates all buffered kv pairs.
func (s *BufferStore) WalkBuffer(f func(k Key, v []byte) error) error {
return errors.Trace(WalkMemBuffer(s.MemBuffer, f))
}
// SaveTo saves all buffered kv pairs into a Mutator.
func (s *BufferStore) SaveTo(m Mutator) error {
err := s.WalkBuffer(func(k Key, v []byte) error {
if len(v) == 0 {
return errors.Trace(m.Delete(k))
}
return errors.Trace(m.Set(k, v))
})
return errors.Trace(err)
}
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