github.com/insionng/yougam@v0.0.0-20170714101924-2bc18d833463/libraries/pingcap/tidb/kv/buffer_store.go (about)

     1  // Copyright 2015 PingCAP, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  package kv
    15  
    16  import (
    17  	"github.com/insionng/yougam/libraries/juju/errors"
    18  )
    19  
    20  // BufferStore wraps a Retriever for read and a MemBuffer for buffered write.
    21  // Common usage pattern:
    22  //	bs := NewBufferStore(r) // use BufferStore to wrap a Retriever
    23  //	defer bs.Release()      // make sure it will be released
    24  //	// ...
    25  //	// read/write on bs
    26  //	// ...
    27  //	bs.SaveTo(m)	        // save above operations to a Mutator
    28  type BufferStore struct {
    29  	MemBuffer
    30  	r Retriever
    31  }
    32  
    33  // NewBufferStore creates a BufferStore using r for read.
    34  func NewBufferStore(r Retriever) *BufferStore {
    35  	return &BufferStore{
    36  		r:         r,
    37  		MemBuffer: &lazyMemBuffer{},
    38  	}
    39  }
    40  
    41  // Get implements the Retriever interface.
    42  func (s *BufferStore) Get(k Key) ([]byte, error) {
    43  	val, err := s.MemBuffer.Get(k)
    44  	if IsErrNotFound(err) {
    45  		val, err = s.r.Get(k)
    46  	}
    47  	if err != nil {
    48  		return nil, errors.Trace(err)
    49  	}
    50  	if len(val) == 0 {
    51  		return nil, errors.Trace(ErrNotExist)
    52  	}
    53  	return val, nil
    54  }
    55  
    56  // Seek implements the Retriever interface.
    57  func (s *BufferStore) Seek(k Key) (Iterator, error) {
    58  	bufferIt, err := s.MemBuffer.Seek(k)
    59  	if err != nil {
    60  		return nil, errors.Trace(err)
    61  	}
    62  	retrieverIt, err := s.r.Seek(k)
    63  	if err != nil {
    64  		return nil, errors.Trace(err)
    65  	}
    66  	return newUnionIter(bufferIt, retrieverIt, false), nil
    67  }
    68  
    69  // SeekReverse implements the Retriever interface.
    70  func (s *BufferStore) SeekReverse(k Key) (Iterator, error) {
    71  	buferIt, err := s.MemBuffer.SeekReverse(k)
    72  	if err != nil {
    73  		return nil, errors.Trace(err)
    74  	}
    75  	retrieverIt, err := s.r.SeekReverse(k)
    76  	if err != nil {
    77  		return nil, errors.Trace(err)
    78  	}
    79  	return newUnionIter(buferIt, retrieverIt, true), nil
    80  }
    81  
    82  // WalkBuffer iterates all buffered kv pairs.
    83  func (s *BufferStore) WalkBuffer(f func(k Key, v []byte) error) error {
    84  	iter, err := s.MemBuffer.Seek(nil)
    85  	if err != nil {
    86  		return errors.Trace(err)
    87  	}
    88  	defer iter.Close()
    89  	for ; iter.Valid(); iter.Next() {
    90  		if err := f(iter.Key(), iter.Value()); err != nil {
    91  			return errors.Trace(err)
    92  		}
    93  	}
    94  	return nil
    95  }
    96  
    97  // SaveTo saves all buffered kv pairs into a Mutator.
    98  func (s *BufferStore) SaveTo(m Mutator) error {
    99  	err := s.WalkBuffer(func(k Key, v []byte) error {
   100  		if len(v) == 0 {
   101  			return errors.Trace(m.Delete(k))
   102  		}
   103  		return errors.Trace(m.Set(k, v))
   104  	})
   105  	return errors.Trace(err)
   106  }