version_edit.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 <set>
#include <utility>
#include <vector>
#include <string>
#include "rocksdb/cache.h"
#include "db/dbformat.h"

namespace rocksdb {

class VersionSet;

// A copyable structure contains information needed to read data from an SST
// file. It can contains a pointer to a table reader opened for the file, or
// file number and size, which can be used to create a new table reader for it.
// The behavior is undefined when a copied of the structure is used when the
// file is not in any live version any more.
struct FileDescriptor {
  uint64_t number;
  uint64_t file_size;  // File size in bytes
  // Table reader in table_reader_handle
  TableReader* table_reader;

  FileDescriptor(uint64_t number, uint64_t file_size)
      : number(number), file_size(file_size), table_reader(nullptr) {}

  uint64_t GetNumber() const { return number; }
  uint64_t GetFileSize() const { return file_size; }
};

struct FileMetaData {
  int refs;
  FileDescriptor fd;
  int allowed_seeks;          // Seeks allowed until compaction
  InternalKey smallest;       // Smallest internal key served by table
  InternalKey largest;        // Largest internal key served by table
  bool being_compacted;       // Is this file undergoing compaction?
  SequenceNumber smallest_seqno;// The smallest seqno in this file
  SequenceNumber largest_seqno; // The largest seqno in this file

  // Needs to be disposed when refs becomes 0.
  Cache::Handle* table_reader_handle;

  FileMetaData()
      : refs(0),
        fd(0, 0),
        allowed_seeks(1 << 30),
        being_compacted(false),
        table_reader_handle(nullptr) {}
};

class VersionEdit {
 public:
  VersionEdit() { Clear(); }
  ~VersionEdit() { }

  void Clear();

  void SetComparatorName(const Slice& name) {
    has_comparator_ = true;
    comparator_ = name.ToString();
  }
  void SetLogNumber(uint64_t num) {
    has_log_number_ = true;
    log_number_ = num;
  }
  void SetPrevLogNumber(uint64_t num) {
    has_prev_log_number_ = true;
    prev_log_number_ = num;
  }
  void SetNextFile(uint64_t num) {
    has_next_file_number_ = true;
    next_file_number_ = num;
  }
  void SetLastSequence(SequenceNumber seq) {
    has_last_sequence_ = true;
    last_sequence_ = seq;
  }
  void SetMaxColumnFamily(uint32_t max_column_family) {
    has_max_column_family_ = true;
    max_column_family_ = max_column_family;
  }

  // Add the specified file at the specified number.
  // REQUIRES: This version has not been saved (see VersionSet::SaveTo)
  // REQUIRES: "smallest" and "largest" are smallest and largest keys in file
  void AddFile(int level, uint64_t file,
               uint64_t file_size,
               const InternalKey& smallest,
               const InternalKey& largest,
               const SequenceNumber& smallest_seqno,
               const SequenceNumber& largest_seqno) {
    assert(smallest_seqno <= largest_seqno);
    FileMetaData f;
    f.fd = FileDescriptor(file, file_size);
    f.smallest = smallest;
    f.largest = largest;
    f.smallest_seqno = smallest_seqno;
    f.largest_seqno = largest_seqno;
    new_files_.push_back(std::make_pair(level, f));
  }

  // Delete the specified "file" from the specified "level".
  void DeleteFile(int level, uint64_t file) {
    deleted_files_.insert({level, file});
  }

  // Number of edits
  int NumEntries() {
    return new_files_.size() + deleted_files_.size();
  }

  bool IsColumnFamilyManipulation() {
    return is_column_family_add_ || is_column_family_drop_;
  }

  void SetColumnFamily(uint32_t column_family_id) {
    column_family_ = column_family_id;
  }

  // set column family ID by calling SetColumnFamily()
  void AddColumnFamily(const std::string& name) {
    assert(!is_column_family_drop_);
    assert(!is_column_family_add_);
    assert(NumEntries() == 0);
    is_column_family_add_ = true;
    column_family_name_ = name;
  }

  // set column family ID by calling SetColumnFamily()
  void DropColumnFamily() {
    assert(!is_column_family_drop_);
    assert(!is_column_family_add_);
    assert(NumEntries() == 0);
    is_column_family_drop_ = true;
  }

  void EncodeTo(std::string* dst) const;
  Status DecodeFrom(const Slice& src);

  std::string DebugString(bool hex_key = false) const;

 private:
  friend class VersionSet;

  typedef std::set< std::pair<int, uint64_t>> DeletedFileSet;

  bool GetLevel(Slice* input, int* level, const char** msg);

  int max_level_;
  std::string comparator_;
  uint64_t log_number_;
  uint64_t prev_log_number_;
  uint64_t next_file_number_;
  uint32_t max_column_family_;
  SequenceNumber last_sequence_;
  bool has_comparator_;
  bool has_log_number_;
  bool has_prev_log_number_;
  bool has_next_file_number_;
  bool has_last_sequence_;
  bool has_max_column_family_;

  DeletedFileSet deleted_files_;
  std::vector<std::pair<int, FileMetaData>> new_files_;

  // Each version edit record should have column_family_id set
  // If it's not set, it is default (0)
  uint32_t column_family_;
  // a version edit can be either column_family add or
  // column_family drop. If it's column family add,
  // it also includes column family name.
  bool is_column_family_drop_;
  bool is_column_family_add_;
  std::string column_family_name_;
};

}  // namespace rocksdb