- // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file. See the AUTHORS file for names of contributors.
-
- #ifndef STORAGE_LEVELDB_DB_DBFORMAT_H_
- #define STORAGE_LEVELDB_DB_DBFORMAT_H_
-
- #include <cstddef>
- #include <cstdint>
- #include <string>
-
- #include "leveldb/comparator.h"
- #include "leveldb/db.h"
- #include "leveldb/filter_policy.h"
- #include "leveldb/slice.h"
- #include "leveldb/table_builder.h"
- #include "util/coding.h"
- #include "util/logging.h"
- #include "iostream"
-
- namespace leveldb {
-
- // Grouping of constants. We may want to make some of these
- // parameters set via options.
- namespace config {
- static const int kNumLevels = 7;
-
- // Level-0 compaction is started when we hit this many files.
- static const int kL0_CompactionTrigger = 4;
-
- // Soft limit on number of level-0 files. We slow down writes at this point.
- static const int kL0_SlowdownWritesTrigger = 8;
-
- // Maximum number of level-0 files. We stop writes at this point.
- static const int kL0_StopWritesTrigger = 12;
-
- // Maximum level to which a new compacted memtable is pushed if it
- // does not create overlap. We try to push to level 2 to avoid the
- // relatively expensive level 0=>1 compactions and to avoid some
- // expensive manifest file operations. We do not push all the way to
- // the largest level since that can generate a lot of wasted disk
- // space if the same key space is being repeatedly overwritten.
- static const int kMaxMemCompactLevel = 2;
-
- // Approximate gap in bytes between samples of data read during iteration.
- static const int kReadBytesPeriod = 1048576;
-
- } // namespace config
-
- class InternalKey;
-
- // Value types encoded as the last component of internal keys.
- // DO NOT CHANGE THESE ENUM VALUES: they are embedded in the on-disk
- // data structures.
- enum ValueType { kTypeDeletion = 0x0, kTypeValue = 0x1 };
- // kValueTypeForSeek defines the ValueType that should be passed when
- // constructing a ParsedInternalKey object for seeking to a particular
- // sequence number (since we sort sequence numbers in decreasing order
- // and the value type is embedded as the low 8 bits in the sequence
- // number in internal keys, we need to use the highest-numbered
- // ValueType, not the lowest).
- static const ValueType kValueTypeForSeek = kTypeValue;
-
- typedef uint64_t SequenceNumber;
-
- // We leave eight bits empty at the bottom so a type and sequence#
- // can be packed together into 64-bits.
- static const SequenceNumber kMaxSequenceNumber = ((0x1ull << 56) - 1);
-
- struct ParsedInternalKey {
- Slice user_key;
- SequenceNumber sequence;
- uint64_t deadTime;
- ValueType type;
-
- ParsedInternalKey() {} // Intentionally left uninitialized (for speed)
- ParsedInternalKey(const Slice& u, const SequenceNumber& seq,
- ValueType t, uint64_t d = 0)
- : user_key(u), sequence(seq), type(t), deadTime(d) {}
- std::string DebugString() const;
- };
-
- // Return the length of the encoding of "key".
- inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {
- return key.user_key.size() + 8 + (key.deadTime != 0) * 8;
- }
-
- // Append the serialization of "key" to *result.
- void AppendInternalKey(std::string* result, const ParsedInternalKey& key);
-
- // Attempt to parse an internal key from "internal_key". On success,
- // stores the parsed data in "*result", and returns true.
- //
- // On error, returns false, leaves "*result" in an undefined state.
- bool ParseInternalKey(const Slice& internal_key, ParsedInternalKey* result);
-
- // Returns the user key portion of an internal key.
- inline Slice ExtractUserKey(const Slice& internal_key) {
- assert(internal_key.size() >= 8);
- uint64_t num = DecodeFixed64(internal_key.data() + internal_key.size() - 8);
- uint8_t havettl = (num & 0xff) >> 1;
- size_t klen = internal_key.size() - 8;
- if(havettl) klen -= 8;
- Slice user_key = Slice(internal_key.data(), klen);
- return user_key;
- }
-
- // A comparator for internal keys that uses a specified comparator for
- // the user key portion and breaks ties by decreasing sequence number.
- class InternalKeyComparator : public Comparator {
- private:
- const Comparator* user_comparator_;
-
- public:
- explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c) {}
- const char* Name() const override;
- int Compare(const Slice& a, const Slice& b) const override;
- void FindShortestSeparator(std::string* start,
- const Slice& limit) const override;
- void FindShortSuccessor(std::string* key) const override;
-
- const Comparator* user_comparator() const { return user_comparator_; }
-
- int Compare(const InternalKey& a, const InternalKey& b) const;
- };
-
- // Filter policy wrapper that converts from internal keys to user keys
- class InternalFilterPolicy : public FilterPolicy {
- private:
- const FilterPolicy* const user_policy_;
-
- public:
- explicit InternalFilterPolicy(const FilterPolicy* p) : user_policy_(p) {}
- const char* Name() const override;
- void CreateFilter(const Slice* keys, int n, std::string* dst) const override;
- bool KeyMayMatch(const Slice& key, const Slice& filter) const override;
- };
-
- // Modules in this directory should keep internal keys wrapped inside
- // the following class instead of plain strings so that we do not
- // incorrectly use string comparisons instead of an InternalKeyComparator.
- class InternalKey {
- private:
- std::string rep_;
-
- public:
- InternalKey() {} // Leave rep_ as empty to indicate it is invalid
- InternalKey(const Slice& user_key, SequenceNumber s,
- ValueType t, uint64_t deadTime = 0) {
- AppendInternalKey(&rep_, ParsedInternalKey(user_key, s, t, deadTime));
- }
-
- bool DecodeFrom(const Slice& s) {
- rep_.assign(s.data(), s.size());
- return !rep_.empty();
- }
-
- Slice Encode() const {
- assert(!rep_.empty());
- return rep_;
- }
-
- Slice user_key() const { return ExtractUserKey(rep_); }
-
- void SetFrom(const ParsedInternalKey& p) {
- rep_.clear();
- AppendInternalKey(&rep_, p);
- }
-
- void Clear() { rep_.clear(); }
-
- std::string DebugString() const;
- };
-
- inline int InternalKeyComparator::Compare(const InternalKey& a,
- const InternalKey& b) const {
- return Compare(a.Encode(), b.Encode());
- }
-
- inline bool ParseInternalKey(const Slice& internal_key,
- ParsedInternalKey* result) {
- const size_t n = internal_key.size();
- if (n < 8) return false;
- uint64_t tag = DecodeFixed64(internal_key.data() + n - 8);
- uint8_t c = tag & 0xff;
- uint8_t havettl = c >> 1;
- assert(havettl <= 0b1);
- result->sequence = tag >> 8;
- result->type = static_cast<ValueType>(c);
- if(havettl){
- result->deadTime = DecodeFixed64(internal_key.data() + n - 16);
- result->user_key = Slice(internal_key.data(), n - 16);
- } else {
- result->deadTime = 0;
- result->user_key = Slice(internal_key.data(), n - 8);
- }
- return (c <= static_cast<uint8_t>(kTypeValue));
- }
-
- // A helper class useful for DBImpl::Get()
- class LookupKey {
- public:
- // Initialize *this for looking up user_key at a snapshot with
- // the specified sequence number.
- LookupKey(const Slice& user_key, SequenceNumber sequence);
-
- LookupKey(const LookupKey&) = delete;
- LookupKey& operator=(const LookupKey&) = delete;
-
- ~LookupKey();
-
- // Return a key suitable for lookup in a MemTable.
- Slice memtable_key() const { return Slice(start_, end_ - start_); }
-
- // Return an internal key (suitable for passing to an internal iterator)
- Slice internal_key() const { return Slice(kstart_, end_ - kstart_); }
-
- // Return the user key
- Slice user_key() const { return Slice(kstart_, end_ - kstart_ - 8); }
-
- private:
- // We construct a char array of the form:
- // klength varint32 <-- start_
- // userkey char[klength] <-- kstart_
- // tag uint64
- // <-- end_
- // The array is a suitable MemTable key.
- // The suffix starting with "userkey" can be used as an InternalKey.
- const char* start_;
- const char* kstart_;
- const char* end_;
- char space_[200]; // Avoid allocation for short keys
- };
-
- inline LookupKey::~LookupKey() {
- if (start_ != space_) delete[] start_;
- }
-
- } // namespace leveldb
-
- #endif // STORAGE_LEVELDB_DB_DBFORMAT_H_
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