From 58841ef12f6cba1bb622353c1fcaa0e3c6fb46c9 Mon Sep 17 00:00:00 2001 From: Ilya Zhuravlev Date: Tue, 23 Oct 2012 01:18:44 +0400 Subject: Add dummy and LevelDB database backends --- src/leveldb/db/dbformat.h | 227 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 227 insertions(+) create mode 100644 src/leveldb/db/dbformat.h (limited to 'src/leveldb/db/dbformat.h') diff --git a/src/leveldb/db/dbformat.h b/src/leveldb/db/dbformat.h new file mode 100644 index 000000000..f7f64dafb --- /dev/null +++ b/src/leveldb/db/dbformat.h @@ -0,0 +1,227 @@ +// 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 +#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(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(c); + result->user_key = Slice(internal_key.data(), n - 8); + return (c <= static_cast(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_ -- cgit v1.2.3