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143 lines
4.1 KiB
C++
143 lines
4.1 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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#ifndef ROCKSDB_LITE
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#include "rocksdb/db.h"
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#include "rocksdb/options.h"
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#include "rocksdb/slice.h"
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#include "rocksdb/utilities/transaction.h"
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#include "rocksdb/utilities/optimistic_transaction_db.h"
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using namespace rocksdb;
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std::string kDBPath = "/tmp/rocksdb_transaction_example";
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int main() {
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// open DB
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Options options;
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options.create_if_missing = true;
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DB* db;
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OptimisticTransactionDB* txn_db;
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Status s = OptimisticTransactionDB::Open(options, kDBPath, &txn_db);
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assert(s.ok());
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db = txn_db->GetBaseDB();
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WriteOptions write_options;
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ReadOptions read_options;
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OptimisticTransactionOptions txn_options;
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std::string value;
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////////////////////////////////////////////////////////
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//
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// Simple OptimisticTransaction Example ("Read Committed")
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//
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////////////////////////////////////////////////////////
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// Start a transaction
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Transaction* txn = txn_db->BeginTransaction(write_options);
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assert(txn);
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// Read a key in this transaction
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s = txn->Get(read_options, "abc", &value);
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assert(s.IsNotFound());
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// Write a key in this transaction
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txn->Put("abc", "def");
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// Read a key OUTSIDE this transaction. Does not affect txn.
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s = db->Get(read_options, "abc", &value);
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// Write a key OUTSIDE of this transaction.
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// Does not affect txn since this is an unrelated key. If we wrote key 'abc'
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// here, the transaction would fail to commit.
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s = db->Put(write_options, "xyz", "zzz");
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// Commit transaction
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s = txn->Commit();
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assert(s.ok());
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delete txn;
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////////////////////////////////////////////////////////
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//
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// "Repeatable Read" (Snapshot Isolation) Example
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// -- Using a single Snapshot
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//
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////////////////////////////////////////////////////////
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// Set a snapshot at start of transaction by setting set_snapshot=true
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txn_options.set_snapshot = true;
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txn = txn_db->BeginTransaction(write_options, txn_options);
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const Snapshot* snapshot = txn->GetSnapshot();
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// Write a key OUTSIDE of transaction
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db->Put(write_options, "abc", "xyz");
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// Read a key using the snapshot
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read_options.snapshot = snapshot;
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s = txn->GetForUpdate(read_options, "abc", &value);
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assert(value == "def");
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// Attempt to commit transaction
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s = txn->Commit();
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// Transaction could not commit since the write outside of the txn conflicted
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// with the read!
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assert(s.IsBusy());
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delete txn;
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// Clear snapshot from read options since it is no longer valid
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read_options.snapshot = nullptr;
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snapshot = nullptr;
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////////////////////////////////////////////////////////
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//
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// "Read Committed" (Monotonic Atomic Views) Example
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// --Using multiple Snapshots
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//
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////////////////////////////////////////////////////////
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// In this example, we set the snapshot multiple times. This is probably
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// only necessary if you have very strict isolation requirements to
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// implement.
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// Set a snapshot at start of transaction
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txn_options.set_snapshot = true;
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txn = txn_db->BeginTransaction(write_options, txn_options);
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// Do some reads and writes to key "x"
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read_options.snapshot = db->GetSnapshot();
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s = txn->Get(read_options, "x", &value);
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txn->Put("x", "x");
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// Do a write outside of the transaction to key "y"
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s = db->Put(write_options, "y", "y");
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// Set a new snapshot in the transaction
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txn->SetSnapshot();
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read_options.snapshot = db->GetSnapshot();
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// Do some reads and writes to key "y"
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s = txn->GetForUpdate(read_options, "y", &value);
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txn->Put("y", "y");
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// Commit. Since the snapshot was advanced, the write done outside of the
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// transaction does not prevent this transaction from Committing.
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s = txn->Commit();
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assert(s.ok());
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delete txn;
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// Clear snapshot from read options since it is no longer valid
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read_options.snapshot = nullptr;
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// Cleanup
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delete txn_db;
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DestroyDB(kDBPath, options);
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return 0;
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}
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#endif // ROCKSDB_LITE
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