ceph/src/rocksdb/examples/transaction_example.cc

   1 // Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #ifndef ROCKSDB_LITE
   7
   8 #include "rocksdb/db.h"
   9 #include "rocksdb/options.h"
  10 #include "rocksdb/slice.h"
  11 #include "rocksdb/utilities/transaction.h"
  12 #include "rocksdb/utilities/transaction_db.h"
  13
  14 using namespace ROCKSDB_NAMESPACE;
  15
  16 #if defined(OS_WIN)
  17 std::string kDBPath = "C:\\Windows\\TEMP\\rocksdb_transaction_example";
  18 #else
  19 std::string kDBPath = "/tmp/rocksdb_transaction_example";
  20 #endif
  21
  22 int main() {
  23   // open DB
  24   Options options;
  25   TransactionDBOptions txn_db_options;
  26   options.create_if_missing = true;
  27   TransactionDB* txn_db;
  28
  29   Status s = TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db);
  30   assert(s.ok());
  31
  32   WriteOptions write_options;
  33   ReadOptions read_options;
  34   TransactionOptions txn_options;
  35   std::string value;
  36
  37   ////////////////////////////////////////////////////////
  38   //
  39   // Simple Transaction Example ("Read Committed")
  40   //
  41   ////////////////////////////////////////////////////////
  42
  43   // Start a transaction
  44   Transaction* txn = txn_db->BeginTransaction(write_options);
  45   assert(txn);
  46
  47   // Read a key in this transaction
  48   s = txn->Get(read_options, "abc", &value);
  49   assert(s.IsNotFound());
  50
  51   // Write a key in this transaction
  52   s = txn->Put("abc", "def");
  53   assert(s.ok());
  54
  55   // Read a key OUTSIDE this transaction. Does not affect txn.
  56   s = txn_db->Get(read_options, "abc", &value);
  57   assert(s.IsNotFound());
  58
  59   // Write a key OUTSIDE of this transaction.
  60   // Does not affect txn since this is an unrelated key.
  61   s = txn_db->Put(write_options, "xyz", "zzz");
  62   assert(s.ok());
  63
  64   // Write a key OUTSIDE of this transaction.
  65   // Fail because the key conflicts with the key written in txn.
  66   s = txn_db->Put(write_options, "abc", "def");
  67   assert(s.subcode() == Status::kLockTimeout);
  68
  69   // Value for key "xyz" has been committed, can be read in txn.
  70   s = txn->Get(read_options, "xyz", &value);
  71   assert(s.ok());
  72   assert(value == "zzz");
  73
  74   // Commit transaction
  75   s = txn->Commit();
  76   assert(s.ok());
  77   delete txn;
  78
  79   // Value is committed, can be read now.
  80   s = txn_db->Get(read_options, "abc", &value);
  81   assert(s.ok());
  82   assert(value == "def");
  83
  84   ////////////////////////////////////////////////////////
  85   //
  86   // "Repeatable Read" (Snapshot Isolation) Example
  87   //   -- Using a single Snapshot
  88   //
  89   ////////////////////////////////////////////////////////
  90
  91   // Set a snapshot at start of transaction by setting set_snapshot=true
  92   txn_options.set_snapshot = true;
  93   txn = txn_db->BeginTransaction(write_options, txn_options);
  94
  95   const Snapshot* snapshot = txn->GetSnapshot();
  96
  97   // Write a key OUTSIDE of transaction
  98   s = txn_db->Put(write_options, "abc", "xyz");
  99   assert(s.ok());
 100
 101   // Read the latest committed value.
 102   s = txn->Get(read_options, "abc", &value);
 103   assert(s.ok());
 104   assert(value == "xyz");
 105
 106   // Read the snapshotted value.
 107   read_options.snapshot = snapshot;
 108   s = txn->Get(read_options, "abc", &value);
 109   assert(s.ok());
 110   assert(value == "def");
 111
 112   // Attempt to read a key using the snapshot.  This will fail since
 113   // the previous write outside this txn conflicts with this read.
 114   s = txn->GetForUpdate(read_options, "abc", &value);
 115   assert(s.IsBusy());
 116
 117   txn->Rollback();
 118
 119   // Snapshot will be released upon deleting the transaction.
 120   delete txn;
 121   // Clear snapshot from read options since it is no longer valid
 122   read_options.snapshot = nullptr;
 123   snapshot = nullptr;
 124
 125   ////////////////////////////////////////////////////////
 126   //
 127   // "Read Committed" (Monotonic Atomic Views) Example
 128   //   --Using multiple Snapshots
 129   //
 130   ////////////////////////////////////////////////////////
 131
 132   // In this example, we set the snapshot multiple times.  This is probably
 133   // only necessary if you have very strict isolation requirements to
 134   // implement.
 135
 136   // Set a snapshot at start of transaction
 137   txn_options.set_snapshot = true;
 138   txn = txn_db->BeginTransaction(write_options, txn_options);
 139
 140   // Do some reads and writes to key "x"
 141   read_options.snapshot = txn_db->GetSnapshot();
 142   s = txn->Get(read_options, "x", &value);
 143   assert(s.IsNotFound());
 144   s = txn->Put("x", "x");
 145   assert(s.ok());
 146
 147   // Do a write outside of the transaction to key "y"
 148   s = txn_db->Put(write_options, "y", "y1");
 149   assert(s.ok());
 150
 151   // Set a new snapshot in the transaction
 152   txn->SetSnapshot();
 153   txn->SetSavePoint();
 154   read_options.snapshot = txn_db->GetSnapshot();
 155
 156   // Do some reads and writes to key "y"
 157   // Since the snapshot was advanced, the write done outside of the
 158   // transaction does not conflict.
 159   s = txn->GetForUpdate(read_options, "y", &value);
 160   assert(s.ok());
 161   assert(value == "y1");
 162   s = txn->Put("y", "y2");
 163   assert(s.ok());
 164
 165   // Decide we want to revert the last write from this transaction.
 166   txn->RollbackToSavePoint();
 167
 168   // Commit.
 169   s = txn->Commit();
 170   assert(s.ok());
 171   delete txn;
 172   // Clear snapshot from read options since it is no longer valid
 173   read_options.snapshot = nullptr;
 174
 175   // db state is at the save point.
 176   s = txn_db->Get(read_options, "x", &value);
 177   assert(s.ok());
 178   assert(value == "x");
 179
 180   s = txn_db->Get(read_options, "y", &value);
 181   assert(s.ok());
 182   assert(value == "y1");
 183
 184   // Cleanup
 185   delete txn_db;
 186   DestroyDB(kDBPath, options);
 187   return 0;
 188 }
 189
 190 #endif  // ROCKSDB_LITE