rocksdb/utilities/transactions/transaction_util.h

// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#ifndef ROCKSDB_LITE

#include <string>
#include <unordered_map>

#include "db/dbformat.h"
#include "db/read_callback.h"

#include "rocksdb/db.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "rocksdb/types.h"

namespace ROCKSDB_NAMESPACE {

struct TransactionKeyMapInfo {
  // Earliest sequence number that is relevant to this transaction for this key
  SequenceNumber seq;

  uint32_t num_writes;
  uint32_t num_reads;

  bool exclusive;

  explicit TransactionKeyMapInfo(SequenceNumber seq_no)
      : seq(seq_no), num_writes(0), num_reads(0), exclusive(false) {}

  // Used in PopSavePoint to collapse two savepoints together.
  void Merge(const TransactionKeyMapInfo& info) {
    assert(seq <= info.seq);
    num_reads += info.num_reads;
    num_writes += info.num_writes;
    exclusive |= info.exclusive;
  }
};

using TransactionKeyMap =
    std::unordered_map<uint32_t,
                       std::unordered_map<std::string, TransactionKeyMapInfo>>;

class DBImpl;
struct SuperVersion;
class WriteBatchWithIndex;

class TransactionUtil {
 public:
  // Verifies there have been no commits to this key in the db since this
  // sequence number.
  //
  // If cache_only is true, then this function will not attempt to read any
  // SST files.  This will make it more likely this function will
  // return an error if it is unable to determine if there are any conflicts.
  //
  // See comment of CheckKey() for explanation of `snap_seq`, `snap_checker`
  // and `min_uncommitted`.
  //
  // Returns OK on success, BUSY if there is a conflicting write, or other error
  // status for any unexpected errors.
  static Status CheckKeyForConflicts(
      DBImpl* db_impl, ColumnFamilyHandle* column_family,
      const std::string& key, SequenceNumber snap_seq, bool cache_only,
      ReadCallback* snap_checker = nullptr,
      SequenceNumber min_uncommitted = kMaxSequenceNumber);

  // For each key,SequenceNumber pair in the TransactionKeyMap, this function
  // will verify there have been no writes to the key in the db since that
  // sequence number.
  //
  // Returns OK on success, BUSY if there is a conflicting write, or other error
  // status for any unexpected errors.
  //
  // REQUIRED: this function should only be called on the write thread or if the
  // mutex is held.
  static Status CheckKeysForConflicts(DBImpl* db_impl,
                                      const TransactionKeyMap& keys,
                                      bool cache_only);

 private:
  // If `snap_checker` == nullptr, writes are always commited in sequence number
  // order. All sequence number <= `snap_seq` will not conflict with any
  // write, and all keys > `snap_seq` of `key` will trigger conflict.
  // If `snap_checker` != nullptr, writes may not commit in sequence number
  // order. In this case `min_uncommitted` is a lower bound.
  //  seq < `min_uncommitted`: no conflict
  //  seq > `snap_seq`: applicable to conflict
  //  `min_uncommitted` <= seq <= `snap_seq`: call `snap_checker` to determine.
  static Status CheckKey(DBImpl* db_impl, SuperVersion* sv,
                         SequenceNumber earliest_seq, SequenceNumber snap_seq,
                         const std::string& key, bool cache_only,
                         ReadCallback* snap_checker = nullptr,
                         SequenceNumber min_uncommitted = kMaxSequenceNumber);
};

}  // namespace ROCKSDB_NAMESPACE

#endif  // ROCKSDB_LITE