memtable.cc raw
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
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
21 MemTable::MemTable(const InternalKeyComparator& comparator)
22 : comparator_(comparator), refs_(0), table_(comparator_, &arena_) {}
23
24 MemTable::~MemTable() { assert(refs_ == 0); }
25
26 size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
27
28 int MemTable::KeyComparator::operator()(const char* aptr,
29 const char* bptr) const {
30 // Internal keys are encoded as length-prefixed strings.
31 Slice a = GetLengthPrefixedSlice(aptr);
32 Slice b = GetLengthPrefixedSlice(bptr);
33 return comparator.Compare(a, b);
34 }
35
36 // Encode a suitable internal key target for "target" and return it.
37 // Uses *scratch as scratch space, and the returned pointer will point
38 // into this scratch space.
39 static const char* EncodeKey(std::string* scratch, const Slice& target) {
40 scratch->clear();
41 PutVarint32(scratch, target.size());
42 scratch->append(target.data(), target.size());
43 return scratch->data();
44 }
45
46 class MemTableIterator : public Iterator {
47 public:
48 explicit MemTableIterator(MemTable::Table* table) : iter_(table) {}
49
50 MemTableIterator(const MemTableIterator&) = delete;
51 MemTableIterator& operator=(const MemTableIterator&) = delete;
52
53 ~MemTableIterator() override = default;
54
55 bool Valid() const override { return iter_.Valid(); }
56 void Seek(const Slice& k) override { iter_.Seek(EncodeKey(&tmp_, k)); }
57 void SeekToFirst() override { iter_.SeekToFirst(); }
58 void SeekToLast() override { iter_.SeekToLast(); }
59 void Next() override { iter_.Next(); }
60 void Prev() override { iter_.Prev(); }
61 Slice key() const override { return GetLengthPrefixedSlice(iter_.key()); }
62 Slice value() const override {
63 Slice key_slice = GetLengthPrefixedSlice(iter_.key());
64 return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
65 }
66
67 Status status() const override { return Status::OK(); }
68
69 private:
70 MemTable::Table::Iterator iter_;
71 std::string tmp_; // For passing to EncodeKey
72 };
73
74 Iterator* MemTable::NewIterator() { return new MemTableIterator(&table_); }
75
76 void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
77 const Slice& value) {
78 // Format of an entry is concatenation of:
79 // key_size : varint32 of internal_key.size()
80 // key bytes : char[internal_key.size()]
81 // value_size : varint32 of value.size()
82 // value bytes : char[value.size()]
83 size_t key_size = key.size();
84 size_t val_size = value.size();
85 size_t internal_key_size = key_size + 8;
86 const size_t encoded_len = VarintLength(internal_key_size) +
87 internal_key_size + VarintLength(val_size) +
88 val_size;
89 char* buf = arena_.Allocate(encoded_len);
90 char* p = EncodeVarint32(buf, internal_key_size);
91 memcpy(p, key.data(), key_size);
92 p += key_size;
93 EncodeFixed64(p, (s << 8) | type);
94 p += 8;
95 p = EncodeVarint32(p, val_size);
96 memcpy(p, value.data(), val_size);
97 assert(p + val_size == buf + encoded_len);
98 table_.Insert(buf);
99 }
100
101 bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
102 Slice memkey = key.memtable_key();
103 Table::Iterator iter(&table_);
104 iter.Seek(memkey.data());
105 if (iter.Valid()) {
106 // entry format is:
107 // klength varint32
108 // userkey char[klength]
109 // tag uint64
110 // vlength varint32
111 // value char[vlength]
112 // Check that it belongs to same user key. We do not check the
113 // sequence number since the Seek() call above should have skipped
114 // all entries with overly large sequence numbers.
115 const char* entry = iter.key();
116 uint32_t key_length;
117 const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
118 if (comparator_.comparator.user_comparator()->Compare(
119 Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
120 // Correct user key
121 const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
122 switch (static_cast<ValueType>(tag & 0xff)) {
123 case kTypeValue: {
124 Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
125 value->assign(v.data(), v.size());
126 return true;
127 }
128 case kTypeDeletion:
129 *s = Status::NotFound(Slice());
130 return true;
131 }
132 }
133 }
134 return false;
135 }
136
137 } // namespace leveldb
138