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-// 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_FORMAT_H_
-#define STORAGE_LEVELDB_DB_FORMAT_H_
-
-#include <stdio.h>
-#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"
-
-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;
-
-} // 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;
- ValueType type;
-
- ParsedInternalKey() { } // Intentionally left uninitialized (for speed)
- ParsedInternalKey(const Slice& u, const SequenceNumber& seq, ValueType t)
- : user_key(u), sequence(seq), type(t) { }
- 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;
-}
-
-// Append the serialization of "key" to *result.
-extern 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.
-extern 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);
- return Slice(internal_key.data(), internal_key.size() - 8);
-}
-
-inline ValueType ExtractValueType(const Slice& internal_key) {
- assert(internal_key.size() >= 8);
- const size_t n = internal_key.size();
- uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
- unsigned char c = num & 0xff;
- return static_cast<ValueType>(c);
-}
-
-// 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) { }
- virtual const char* Name() const;
- virtual int Compare(const Slice& a, const Slice& b) const;
- virtual void FindShortestSeparator(
- std::string* start,
- const Slice& limit) const;
- virtual void FindShortSuccessor(std::string* key) const;
-
- 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) { }
- virtual const char* Name() const;
- virtual void CreateFilter(const Slice* keys, int n, std::string* dst) const;
- virtual bool KeyMayMatch(const Slice& key, const Slice& filter) const;
-};
-
-// 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) {
- AppendInternalKey(&rep_, ParsedInternalKey(user_key, s, t));
- }
-
- void DecodeFrom(const Slice& s) { rep_.assign(s.data(), s.size()); }
- 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 num = DecodeFixed64(internal_key.data() + n - 8);
- unsigned char c = num & 0xff;
- result->sequence = num >> 8;
- result->type = static_cast<ValueType>(c);
- result->user_key = Slice(internal_key.data(), n - 8);
- return (c <= static_cast<unsigned char>(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();
-
- // 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
-
- // No copying allowed
- LookupKey(const LookupKey&);
- void operator=(const LookupKey&);
-};
-
-inline LookupKey::~LookupKey() {
- if (start_ != space_) delete[] start_;
-}
-
-} // namespace leveldb
-
-#endif // STORAGE_LEVELDB_DB_FORMAT_H_