// 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).
#ifndef ROCKSDB_LITE
#include "rocksdb/db.h"
#include "rocksdb/options.h"
#include "rocksdb/slice.h"
#include "rocksdb/utilities/transaction.h"
#include "rocksdb/utilities/optimistic_transaction_db.h"
using
namespace
rocksdb;
std::string kDBPath =
"/tmp/rocksdb_transaction_example"
;
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
txn->Put(
"abc"
,
"def"
);
// Read a key OUTSIDE this transaction. Does not affect txn.
s = db->Get(read_options,
"abc"
, &value);
// 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"
);
// Commit transaction
s = txn->Commit();
assert
(s.ok());
delete
txn;
////////////////////////////////////////////////////////
//
// "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
db->Put(write_options,
"abc"
,
"xyz"
);
// Read a key using the snapshot
read_options.snapshot = snapshot;
s = txn->GetForUpdate(read_options,
"abc"
, &value);
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
;
////////////////////////////////////////////////////////
//
// "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);
txn->Put(
"x"
,
"x"
);
// Do a write outside of the transaction to key "y"
s = db->Put(write_options,
"y"
,
"y"
);
// 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);
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
;
// Cleanup
delete
txn_db;
DestroyDB(kDBPath, options);
return
0;
}
#endif // ROCKSDB_LITE