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// 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).
#include "rocksdb/db.h"
#include "rocksdb/options.h"
#include "rocksdb/slice.h"
#include "rocksdb/utilities/optimistic_transaction_db.h"
#include "rocksdb/utilities/transaction.h"
using ROCKSDB_NAMESPACE::DB;
using ROCKSDB_NAMESPACE::OptimisticTransactionDB;
using ROCKSDB_NAMESPACE::OptimisticTransactionOptions;
using ROCKSDB_NAMESPACE::Options;
using ROCKSDB_NAMESPACE::ReadOptions;
using ROCKSDB_NAMESPACE::Snapshot;
using ROCKSDB_NAMESPACE::Status;
using ROCKSDB_NAMESPACE::Transaction;
using ROCKSDB_NAMESPACE::WriteOptions;
#if defined(OS_WIN)
std::string kDBPath = "C:\\Windows\\TEMP\\rocksdb_transaction_example";
#else
std::string kDBPath = "/tmp/rocksdb_transaction_example";
#endif
int main() {
// open DB
Options options;
options.create_if_missing = true;
DB* db;
OptimisticTransactionDB* txn_db;
Status s = OptimisticTransactionDB::Open(options, kDBPath, &txn_db);
assert(s.ok());
db = txn_db->GetBaseDB();
WriteOptions write_options;
ReadOptions read_options;
OptimisticTransactionOptions txn_options;
std::string value;
////////////////////////////////////////////////////////
//
// Simple OptimisticTransaction Example ("Read Committed")
//
////////////////////////////////////////////////////////
// Start a transaction
Transaction* txn = txn_db->BeginTransaction(write_options);
assert(txn);
// Read a key in this transaction
s = txn->Get(read_options, "abc", &value);
assert(s.IsNotFound());
// Write a key in this transaction
s = txn->Put("abc", "xyz");
assert(s.ok());
// Read a key OUTSIDE this transaction. Does not affect txn.
s = db->Get(read_options, "abc", &value);
assert(s.IsNotFound());
// Write a key OUTSIDE of this transaction.
// Does not affect txn since this is an unrelated key. If we wrote key 'abc'
// here, the transaction would fail to commit.
s = db->Put(write_options, "xyz", "zzz");
assert(s.ok());
s = db->Put(write_options, "abc", "def");
assert(s.ok());
// Commit transaction
s = txn->Commit();
assert(s.IsBusy());
delete txn;
s = db->Get(read_options, "xyz", &value);
assert(s.ok());
assert(value == "zzz");
s = db->Get(read_options, "abc", &value);
assert(s.ok());
assert(value == "def");
////////////////////////////////////////////////////////
//
// "Repeatable Read" (Snapshot Isolation) Example
// -- Using a single Snapshot
//
////////////////////////////////////////////////////////
// Set a snapshot at start of transaction by setting set_snapshot=true
txn_options.set_snapshot = true;
txn = txn_db->BeginTransaction(write_options, txn_options);
const Snapshot* snapshot = txn->GetSnapshot();
// Write a key OUTSIDE of transaction
s = db->Put(write_options, "abc", "xyz");
assert(s.ok());
// Read a key using the snapshot
read_options.snapshot = snapshot;
s = txn->GetForUpdate(read_options, "abc", &value);
assert(s.ok());
assert(value == "def");
// Attempt to commit transaction
s = txn->Commit();
// Transaction could not commit since the write outside of the txn conflicted
// with the read!
assert(s.IsBusy());
delete txn;
// Clear snapshot from read options since it is no longer valid
read_options.snapshot = nullptr;
snapshot = nullptr;
s = db->Get(read_options, "abc", &value);
assert(s.ok());
assert(value == "xyz");
////////////////////////////////////////////////////////
//
// "Read Committed" (Monotonic Atomic Views) Example
// --Using multiple Snapshots
//
////////////////////////////////////////////////////////
// In this example, we set the snapshot multiple times. This is probably
// only necessary if you have very strict isolation requirements to
// implement.
// Set a snapshot at start of transaction
txn_options.set_snapshot = true;
txn = txn_db->BeginTransaction(write_options, txn_options);
// Do some reads and writes to key "x"
read_options.snapshot = db->GetSnapshot();
s = txn->Get(read_options, "x", &value);
assert(s.IsNotFound());
s = txn->Put("x", "x");
assert(s.ok());
// The transaction hasn't committed, so the write is not visible
// outside of txn.
s = db->Get(read_options, "x", &value);
assert(s.IsNotFound());
// Do a write outside of the transaction to key "y"
s = db->Put(write_options, "y", "z");
assert(s.ok());
// Set a new snapshot in the transaction
txn->SetSnapshot();
read_options.snapshot = db->GetSnapshot();
// Do some reads and writes to key "y"
s = txn->GetForUpdate(read_options, "y", &value);
assert(s.ok());
assert(value == "z");
txn->Put("y", "y");
// Commit. Since the snapshot was advanced, the write done outside of the
// transaction does not prevent this transaction from Committing.
s = txn->Commit();
assert(s.ok());
delete txn;
// Clear snapshot from read options since it is no longer valid
read_options.snapshot = nullptr;
// txn is committed, read the latest values.
s = db->Get(read_options, "x", &value);
assert(s.ok());
assert(value == "x");
s = db->Get(read_options, "y", &value);
assert(s.ok());
assert(value == "y");
// Cleanup
delete txn_db;
DestroyDB(kDBPath, options);
return 0;
}
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