github.com/whtcorpsinc/MilevaDB-Prod@v0.0.0-20211104133533-f57f4be3b597/allegrosql/memdb_snapshot.go (about)

     1  // Copyright 2020 WHTCORPS INC, 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 ekv
    15  
    16  import "context"
    17  
    18  func (EDB *memdb) SnapshotGetter() Getter {
    19  	return &memdbSnapGetter{
    20  		EDB: EDB,
    21  		cp:  EDB.getSnapshot(),
    22  	}
    23  }
    24  
    25  func (EDB *memdb) SnapshotIter(start, end Key) Iterator {
    26  	it := &memdbSnapIter{
    27  		memdbIterator: &memdbIterator{
    28  			EDB:   EDB,
    29  			start: start,
    30  			end:   end,
    31  		},
    32  		cp: EDB.getSnapshot(),
    33  	}
    34  	it.init()
    35  	return it
    36  }
    37  
    38  func (EDB *memdb) getSnapshot() memdbCheckpoint {
    39  	if len(EDB.stages) > 0 {
    40  		return EDB.stages[0]
    41  	}
    42  	return EDB.vlog.checkpoint()
    43  }
    44  
    45  type memdbSnapGetter struct {
    46  	EDB *memdb
    47  	cp  memdbCheckpoint
    48  }
    49  
    50  func (snap *memdbSnapGetter) Get(_ context.Context, key Key) ([]byte, error) {
    51  	x := snap.EDB.traverse(key, false)
    52  	if x.isNull() {
    53  		return nil, ErrNotExist
    54  	}
    55  	if x.vptr.isNull() {
    56  		// A flag only key, act as value not exists
    57  		return nil, ErrNotExist
    58  	}
    59  	v, ok := snap.EDB.vlog.getSnapshotValue(x.vptr, &snap.cp)
    60  	if !ok {
    61  		return nil, ErrNotExist
    62  	}
    63  	return v, nil
    64  }
    65  
    66  type memdbSnapIter struct {
    67  	*memdbIterator
    68  	value []byte
    69  	cp    memdbCheckpoint
    70  }
    71  
    72  func (i *memdbSnapIter) Value() []byte {
    73  	return i.value
    74  }
    75  
    76  func (i *memdbSnapIter) Next() error {
    77  	i.value = nil
    78  	for i.Valid() {
    79  		if err := i.memdbIterator.Next(); err != nil {
    80  			return err
    81  		}
    82  		if i.setValue() {
    83  			return nil
    84  		}
    85  	}
    86  	return nil
    87  }
    88  
    89  func (i *memdbSnapIter) setValue() bool {
    90  	if !i.Valid() {
    91  		return false
    92  	}
    93  	if v, ok := i.EDB.vlog.getSnapshotValue(i.curr.vptr, &i.cp); ok {
    94  		i.value = v
    95  		return true
    96  	}
    97  	return false
    98  }
    99  
   100  func (i *memdbSnapIter) init() {
   101  	if len(i.start) == 0 {
   102  		i.seekToFirst()
   103  	} else {
   104  		i.seek(i.start)
   105  	}
   106  
   107  	if !i.setValue() {
   108  		err := i.Next()
   109  		_ = err // memdbIterator will never fail
   110  	}
   111  }