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 #ifndef STORAGE_LEVELDB_DB_FORMAT_H_
6 #define STORAGE_LEVELDB_DB_FORMAT_H_
9 #include "leveldb/comparator.h"
10 #include "leveldb/db.h"
11 #include "leveldb/slice.h"
12 #include "leveldb/table_builder.h"
13 #include "util/coding.h"
14 #include "util/logging.h"
18 // Grouping of constants. We may want to make some of these
19 // parameters set via options.
21 static const int kNumLevels = 7;
23 // Level-0 compaction is started when we hit this many files.
24 static const int kL0_CompactionTrigger = 4;
26 // Soft limit on number of level-0 files. We slow down writes at this point.
27 static const int kL0_SlowdownWritesTrigger = 8;
29 // Maximum number of level-0 files. We stop writes at this point.
30 static const int kL0_StopWritesTrigger = 12;
32 // Maximum level to which a new compacted memtable is pushed if it
33 // does not create overlap. We try to push to level 2 to avoid the
34 // relatively expensive level 0=>1 compactions and to avoid some
35 // expensive manifest file operations. We do not push all the way to
36 // the largest level since that can generate a lot of wasted disk
37 // space if the same key space is being repeatedly overwritten.
38 static const int kMaxMemCompactLevel = 2;
44 // Value types encoded as the last component of internal keys.
45 // DO NOT CHANGE THESE ENUM VALUES: they are embedded in the on-disk
51 // kValueTypeForSeek defines the ValueType that should be passed when
52 // constructing a ParsedInternalKey object for seeking to a particular
53 // sequence number (since we sort sequence numbers in decreasing order
54 // and the value type is embedded as the low 8 bits in the sequence
55 // number in internal keys, we need to use the highest-numbered
56 // ValueType, not the lowest).
57 static const ValueType kValueTypeForSeek = kTypeValue;
59 typedef uint64_t SequenceNumber;
61 // We leave eight bits empty at the bottom so a type and sequence#
62 // can be packed together into 64-bits.
63 static const SequenceNumber kMaxSequenceNumber =
66 struct ParsedInternalKey {
68 SequenceNumber sequence;
71 ParsedInternalKey() { } // Intentionally left uninitialized (for speed)
72 ParsedInternalKey(const Slice& u, const SequenceNumber& seq, ValueType t)
73 : user_key(u), sequence(seq), type(t) { }
74 std::string DebugString() const;
77 // Return the length of the encoding of "key".
78 inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {
79 return key.user_key.size() + 8;
82 // Append the serialization of "key" to *result.
83 extern void AppendInternalKey(std::string* result,
84 const ParsedInternalKey& key);
86 // Attempt to parse an internal key from "internal_key". On success,
87 // stores the parsed data in "*result", and returns true.
89 // On error, returns false, leaves "*result" in an undefined state.
90 extern bool ParseInternalKey(const Slice& internal_key,
91 ParsedInternalKey* result);
93 // Returns the user key portion of an internal key.
94 inline Slice ExtractUserKey(const Slice& internal_key) {
95 assert(internal_key.size() >= 8);
96 return Slice(internal_key.data(), internal_key.size() - 8);
99 inline ValueType ExtractValueType(const Slice& internal_key) {
100 assert(internal_key.size() >= 8);
101 const size_t n = internal_key.size();
102 uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
103 unsigned char c = num & 0xff;
104 return static_cast<ValueType>(c);
107 // A comparator for internal keys that uses a specified comparator for
108 // the user key portion and breaks ties by decreasing sequence number.
109 class InternalKeyComparator : public Comparator {
111 const Comparator* user_comparator_;
113 explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c) { }
114 virtual const char* Name() const;
115 virtual int Compare(const Slice& a, const Slice& b) const;
116 virtual void FindShortestSeparator(
118 const Slice& limit) const;
119 virtual void FindShortSuccessor(std::string* key) const;
121 const Comparator* user_comparator() const { return user_comparator_; }
123 int Compare(const InternalKey& a, const InternalKey& b) const;
126 // Modules in this directory should keep internal keys wrapped inside
127 // the following class instead of plain strings so that we do not
128 // incorrectly use string comparisons instead of an InternalKeyComparator.
133 InternalKey() { } // Leave rep_ as empty to indicate it is invalid
134 InternalKey(const Slice& user_key, SequenceNumber s, ValueType t) {
135 AppendInternalKey(&rep_, ParsedInternalKey(user_key, s, t));
138 void DecodeFrom(const Slice& s) { rep_.assign(s.data(), s.size()); }
139 Slice Encode() const {
140 assert(!rep_.empty());
144 Slice user_key() const { return ExtractUserKey(rep_); }
146 void SetFrom(const ParsedInternalKey& p) {
148 AppendInternalKey(&rep_, p);
151 void Clear() { rep_.clear(); }
153 std::string DebugString() const;
156 inline int InternalKeyComparator::Compare(
157 const InternalKey& a, const InternalKey& b) const {
158 return Compare(a.Encode(), b.Encode());
161 inline bool ParseInternalKey(const Slice& internal_key,
162 ParsedInternalKey* result) {
163 const size_t n = internal_key.size();
164 if (n < 8) return false;
165 uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
166 unsigned char c = num & 0xff;
167 result->sequence = num >> 8;
168 result->type = static_cast<ValueType>(c);
169 result->user_key = Slice(internal_key.data(), n - 8);
170 return (c <= static_cast<unsigned char>(kTypeValue));
173 // A helper class useful for DBImpl::Get()
176 // Initialize *this for looking up user_key at a snapshot with
177 // the specified sequence number.
178 LookupKey(const Slice& user_key, SequenceNumber sequence);
182 // Return a key suitable for lookup in a MemTable.
183 Slice memtable_key() const { return Slice(start_, end_ - start_); }
185 // Return an internal key (suitable for passing to an internal iterator)
186 Slice internal_key() const { return Slice(kstart_, end_ - kstart_); }
188 // Return the user key
189 Slice user_key() const { return Slice(kstart_, end_ - kstart_ - 8); }
192 // We construct a char array of the form:
193 // klength varint32 <-- start_
194 // userkey char[klength] <-- kstart_
197 // The array is a suitable MemTable key.
198 // The suffix starting with "userkey" can be used as an InternalKey.
202 char space_[200]; // Avoid allocation for short keys
204 // No copying allowed
205 LookupKey(const LookupKey&);
206 void operator=(const LookupKey&);
209 inline LookupKey::~LookupKey() {
210 if (start_ != space_) delete[] start_;
213 } // namespace leveldb
215 #endif // STORAGE_LEVELDB_DB_FORMAT_H_