rocksdb/db/dbformat.h

//  Copyright (c) 2013, Facebook, Inc.  All rights reserved.
//  This source code is licensed under the BSD-style license found in the
//  LICENSE file in the root directory of this source tree. An additional grant
//  of patent rights can be found in the PATENTS file in the same directory.
//
// 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.

#pragma once
#include <stdio.h>
#include "rocksdb/comparator.h"
#include "rocksdb/db.h"
#include "rocksdb/filter_policy.h"
#include "rocksdb/slice.h"
#include "rocksdb/table.h"
#include "rocksdb/types.h"
#include "util/coding.h"
#include "util/logging.h"

namespace rocksdb {

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.
// The highest bit of the value type needs to be reserved to SST tables
// for them to do more flexible encoding.
enum ValueType : unsigned char {
  kTypeDeletion = 0x0,
  kTypeValue = 0x1,
  kTypeMerge = 0x2,
  kTypeLogData = 0x3,
  kMaxValue = 0x7F
};

// 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 = kTypeMerge;

// 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(bool hex = false) const;
};

// Return the length of the encoding of "key".
inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {
  return key.user_key.size() + 8;
}

extern uint64_t PackSequenceAndType(uint64_t seq, ValueType t);

// 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_;
  std::string name_;
 public:
  explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c),
    name_("rocksdb.InternalKeyComparator:" +
          std::string(user_comparator_->Name())) {
  }
  virtual ~InternalKeyComparator() {}

  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;
  int Compare(const ParsedInternalKey& a, const ParsedInternalKey& 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(bool hex = false) 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);
  assert(result->type <= ValueType::kMaxValue);
  result->user_key = Slice(internal_key.data(), n - 8);
  return (c <= static_cast<unsigned char>(kValueTypeForSeek));
}

// Update the sequence number in the internal key
inline void UpdateInternalKey(char* internal_key,
                              const size_t internal_key_size,
                              uint64_t seq, ValueType t) {
  assert(internal_key_size >= 8);
  char* seqtype = internal_key + internal_key_size - 8;
  uint64_t newval = (seq << 8) | t;
  EncodeFixed64(seqtype, newval);
}

// Get the sequence number from the internal key
inline uint64_t GetInternalKeySeqno(const Slice& internal_key) {
  const size_t n = internal_key.size();
  assert(n >= 8);
  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
  return num >> 8;
}


// 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_;
}

class IterKey {
 public:
  IterKey() : key_(space_), buf_size_(sizeof(space_)), key_size_(0) {}

  ~IterKey() { Clear(); }

  Slice GetKey() const {
    if (key_ != nullptr) {
      return Slice(key_, key_size_);
    } else {
      return Slice();
    }
  }

  bool Valid() const { return key_ != nullptr; }

  void Clear() {
    if (key_ != nullptr && key_ != space_) {
      delete[] key_;
    }
    key_ = space_;
    buf_size_ = sizeof(buf_size_);
  }

  // Enlarge the buffer size if needed based on key_size.
  // By default, static allocated buffer is used. Once there is a key
  // larger than the static allocated buffer, another buffer is dynamically
  // allocated, until a larger key buffer is requested. In that case, we
  // reallocate buffer and delete the old one.
  void EnlargeBufferIfNeeded(size_t key_size) {
    // If size is smaller than buffer size, continue using current buffer,
    // or the static allocated one, as default
    if (key_size > buf_size_) {
      // Need to enlarge the buffer.
      Clear();
      key_ = new char[key_size];
      buf_size_ = key_size;
    }
    key_size_ = key_size;
  }

  void SetUserKey(const Slice& user_key) {
    size_t size = user_key.size();
    EnlargeBufferIfNeeded(size);
    memcpy(key_, user_key.data(), size);
  }

  void SetInternalKey(const Slice& user_key, SequenceNumber s,
                      ValueType value_type = kValueTypeForSeek) {
    size_t usize = user_key.size();
    EnlargeBufferIfNeeded(usize + sizeof(uint64_t));
    memcpy(key_, user_key.data(), usize);
    EncodeFixed64(key_ + usize, PackSequenceAndType(s, value_type));
  }

  void SetInternalKey(const ParsedInternalKey& parsed_key) {
    SetInternalKey(parsed_key.user_key, parsed_key.sequence, parsed_key.type);
  }

 private:
  char* key_;
  size_t buf_size_;
  size_t key_size_;
  char space_[32];  // Avoid allocation for short keys

  // No copying allowed
  IterKey(const IterKey&) = delete;
  void operator=(const IterKey&) = delete;
};

}  // namespace rocksdb