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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/transaction.h"
#include "rocksdb/utilities/transaction_db.h"
using ROCKSDB_NAMESPACE::Options;
using ROCKSDB_NAMESPACE::ReadOptions;
using ROCKSDB_NAMESPACE::Snapshot;
using ROCKSDB_NAMESPACE::Status;
using ROCKSDB_NAMESPACE::Transaction;
using ROCKSDB_NAMESPACE::TransactionDB;
using ROCKSDB_NAMESPACE::TransactionDBOptions;
using ROCKSDB_NAMESPACE::TransactionOptions;
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;
TransactionDBOptions txn_db_options;
options.create_if_missing = true;
TransactionDB* txn_db;
Status s = TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db);
assert(s.ok());
WriteOptions write_options;
ReadOptions read_options;
TransactionOptions txn_options;
std::string value;
////////////////////////////////////////////////////////
//
// Simple Transaction 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", "def");
assert(s.ok());
// Read a key OUTSIDE this transaction. Does not affect txn.
s = txn_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.
s = txn_db->Put(write_options, "xyz", "zzz");
assert(s.ok());
// Write a key OUTSIDE of this transaction.
// Fail because the key conflicts with the key written in txn.
s = txn_db->Put(write_options, "abc", "def");
assert(s.subcode() == Status::kLockTimeout);
// Value for key "xyz" has been committed, can be read in txn.
s = txn->Get(read_options, "xyz", &value);
assert(s.ok());
assert(value == "zzz");
// Commit transaction
s = txn->Commit();
assert(s.ok());
delete txn;
// Value is committed, can be read now.
s = txn_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 = txn_db->Put(write_options, "abc", "xyz");
assert(s.ok());
// Read the latest committed value.
s = txn->Get(read_options, "abc", &value);
assert(s.ok());
assert(value == "xyz");
// Read the snapshotted value.
read_options.snapshot = snapshot;
s = txn->Get(read_options, "abc", &value);
assert(s.ok());
assert(value == "def");
// Attempt to read a key using the snapshot. This will fail since
// the previous write outside this txn conflicts with this read.
s = txn->GetForUpdate(read_options, "abc", &value);
assert(s.IsBusy());
txn->Rollback();
// Snapshot will be released upon deleting the transaction.
delete txn;
// Clear snapshot from read options since it is no longer valid
read_options.snapshot = nullptr;
snapshot = nullptr;
////////////////////////////////////////////////////////
//
// "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 = txn_db->GetSnapshot();
s = txn->Get(read_options, "x", &value);
assert(s.IsNotFound());
s = txn->Put("x", "x");
assert(s.ok());
// Do a write outside of the transaction to key "y"
s = txn_db->Put(write_options, "y", "y1");
assert(s.ok());
// Set a new snapshot in the transaction
txn->SetSnapshot();
txn->SetSavePoint();
read_options.snapshot = txn_db->GetSnapshot();
// Do some reads and writes to key "y"
// Since the snapshot was advanced, the write done outside of the
// transaction does not conflict.
s = txn->GetForUpdate(read_options, "y", &value);
assert(s.ok());
assert(value == "y1");
s = txn->Put("y", "y2");
assert(s.ok());
// Decide we want to revert the last write from this transaction.
txn->RollbackToSavePoint();
// Commit.
s = txn->Commit();
assert(s.ok());
delete txn;
// Clear snapshot from read options since it is no longer valid
read_options.snapshot = nullptr;
// db state is at the save point.
s = txn_db->Get(read_options, "x", &value);
assert(s.ok());
assert(value == "x");
s = txn_db->Get(read_options, "y", &value);
assert(s.ok());
assert(value == "y1");
// Cleanup
delete txn_db;
ROCKSDB_NAMESPACE::DestroyDB(kDBPath, options);
return 0;
}
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