1 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5 #include "db/memtable.h"
6 #include "db/dbformat.h"
7 #include "leveldb/comparator.h"
8 #include "leveldb/env.h"
9 #include "leveldb/iterator.h"
10 #include "util/coding.h"
11
12 namespace leveldb {
13
GetLengthPrefixedSlice(const char * data)14 static Slice GetLengthPrefixedSlice(const char* data) {
15 uint32_t len;
16 const char* p = data;
17 p = GetVarint32Ptr(p, p + 5, &len); // +5: we assume "p" is not corrupted
18 return Slice(p, len);
19 }
20
MemTable(const InternalKeyComparator & cmp)21 MemTable::MemTable(const InternalKeyComparator& cmp)
22 : comparator_(cmp),
23 refs_(0),
24 table_(comparator_, &arena_) {
25 }
26
~MemTable()27 MemTable::~MemTable() {
28 assert(refs_ == 0);
29 }
30
ApproximateMemoryUsage()31 size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
32
operator ()(const char * aptr,const char * bptr) const33 int MemTable::KeyComparator::operator()(const char* aptr, const char* bptr)
34 const {
35 // Internal keys are encoded as length-prefixed strings.
36 Slice a = GetLengthPrefixedSlice(aptr);
37 Slice b = GetLengthPrefixedSlice(bptr);
38 return comparator.Compare(a, b);
39 }
40
41 // Encode a suitable internal key target for "target" and return it.
42 // Uses *scratch as scratch space, and the returned pointer will point
43 // into this scratch space.
EncodeKey(std::string * scratch,const Slice & target)44 static const char* EncodeKey(std::string* scratch, const Slice& target) {
45 scratch->clear();
46 PutVarint32(scratch, target.size());
47 scratch->append(target.data(), target.size());
48 return scratch->data();
49 }
50
51 class MemTableIterator: public Iterator {
52 public:
MemTableIterator(MemTable::Table * table)53 explicit MemTableIterator(MemTable::Table* table) : iter_(table) { }
54
Valid() const55 virtual bool Valid() const { return iter_.Valid(); }
Seek(const Slice & k)56 virtual void Seek(const Slice& k) { iter_.Seek(EncodeKey(&tmp_, k)); }
SeekToFirst()57 virtual void SeekToFirst() { iter_.SeekToFirst(); }
SeekToLast()58 virtual void SeekToLast() { iter_.SeekToLast(); }
Next()59 virtual void Next() { iter_.Next(); }
Prev()60 virtual void Prev() { iter_.Prev(); }
key() const61 virtual Slice key() const { return GetLengthPrefixedSlice(iter_.key()); }
value() const62 virtual Slice value() const {
63 Slice key_slice = GetLengthPrefixedSlice(iter_.key());
64 return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
65 }
66
status() const67 virtual Status status() const { return Status::OK(); }
68
69 private:
70 MemTable::Table::Iterator iter_;
71 std::string tmp_; // For passing to EncodeKey
72
73 // No copying allowed
74 MemTableIterator(const MemTableIterator&);
75 void operator=(const MemTableIterator&);
76 };
77
NewIterator()78 Iterator* MemTable::NewIterator() {
79 return new MemTableIterator(&table_);
80 }
81
Add(SequenceNumber s,ValueType type,const Slice & key,const Slice & value)82 void MemTable::Add(SequenceNumber s, ValueType type,
83 const Slice& key,
84 const Slice& value) {
85 // Format of an entry is concatenation of:
86 // key_size : varint32 of internal_key.size()
87 // key bytes : char[internal_key.size()]
88 // value_size : varint32 of value.size()
89 // value bytes : char[value.size()]
90 size_t key_size = key.size();
91 size_t val_size = value.size();
92 size_t internal_key_size = key_size + 8;
93 const size_t encoded_len =
94 VarintLength(internal_key_size) + internal_key_size +
95 VarintLength(val_size) + val_size;
96 char* buf = arena_.Allocate(encoded_len);
97 char* p = EncodeVarint32(buf, internal_key_size);
98 memcpy(p, key.data(), key_size);
99 p += key_size;
100 EncodeFixed64(p, (s << 8) | type);
101 p += 8;
102 p = EncodeVarint32(p, val_size);
103 memcpy(p, value.data(), val_size);
104 assert((p + val_size) - buf == encoded_len);
105 table_.Insert(buf);
106 }
107
Get(const LookupKey & key,std::string * value,Status * s)108 bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
109 Slice memkey = key.memtable_key();
110 Table::Iterator iter(&table_);
111 iter.Seek(memkey.data());
112 if (iter.Valid()) {
113 // entry format is:
114 // klength varint32
115 // userkey char[klength]
116 // tag uint64
117 // vlength varint32
118 // value char[vlength]
119 // Check that it belongs to same user key. We do not check the
120 // sequence number since the Seek() call above should have skipped
121 // all entries with overly large sequence numbers.
122 const char* entry = iter.key();
123 uint32_t key_length;
124 const char* key_ptr = GetVarint32Ptr(entry, entry+5, &key_length);
125 if (comparator_.comparator.user_comparator()->Compare(
126 Slice(key_ptr, key_length - 8),
127 key.user_key()) == 0) {
128 // Correct user key
129 const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
130 switch (static_cast<ValueType>(tag & 0xff)) {
131 case kTypeValue: {
132 Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
133 value->assign(v.data(), v.size());
134 return true;
135 }
136 case kTypeDeletion:
137 *s = Status::NotFound(Slice());
138 return true;
139 }
140 }
141 }
142 return false;
143 }
144
145 } // namespace leveldb
146