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.
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"
14 static Slice GetLengthPrefixedSlice(const char* data) {
17 p = GetVarint32Ptr(p, p + 5, &len); // +5: we assume "p" is not corrupted
21 MemTable::MemTable(const InternalKeyComparator& cmp)
24 table_(comparator_, &arena_) {
27 MemTable::~MemTable() {
31 size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
33 int MemTable::KeyComparator::operator()(const char* aptr, const char* bptr)
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);
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.
44 static const char* EncodeKey(std::string* scratch, const Slice& target) {
46 PutVarint32(scratch, target.size());
47 scratch->append(target.data(), target.size());
48 return scratch->data();
51 class MemTableIterator: public Iterator {
53 explicit MemTableIterator(MemTable::Table* table) : iter_(table) { }
55 virtual bool Valid() const { return iter_.Valid(); }
56 virtual void Seek(const Slice& k) { iter_.Seek(EncodeKey(&tmp_, k)); }
57 virtual void SeekToFirst() { iter_.SeekToFirst(); }
58 virtual void SeekToLast() { iter_.SeekToLast(); }
59 virtual void Next() { iter_.Next(); }
60 virtual void Prev() { iter_.Prev(); }
61 virtual Slice key() const { return GetLengthPrefixedSlice(iter_.key()); }
62 virtual Slice value() const {
63 Slice key_slice = GetLengthPrefixedSlice(iter_.key());
64 return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
67 virtual Status status() const { return Status::OK(); }
70 MemTable::Table::Iterator iter_;
71 std::string tmp_; // For passing to EncodeKey
74 MemTableIterator(const MemTableIterator&);
75 void operator=(const MemTableIterator&);
78 Iterator* MemTable::NewIterator() {
79 return new MemTableIterator(&table_);
82 void MemTable::Add(SequenceNumber s, ValueType type,
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);
100 EncodeFixed64(p, (s << 8) | type);
102 p = EncodeVarint32(p, val_size);
103 memcpy(p, value.data(), val_size);
104 assert((p + val_size) - buf == encoded_len);
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());
115 // userkey char[klength]
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();
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) {
129 const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
130 switch (static_cast<ValueType>(tag & 0xff)) {
132 Slice v = GetLengthPrefixedSlice(key_ptr + key_length);
133 value->assign(v.data(), v.size());
137 *s = Status::NotFound(Slice());
145 } // namespace leveldb