Author: mysqlpp
Date: Thu Apr 30 04:23:52 2009
New Revision: 2511
URL: http://svn.gna.org/viewcvs/mysqlpp?rev=2511&view=rev
Log:
Added a feature to Transaction, where it can send a SET TRANSACTION
ISOLATION LEVEL query before it starts the transaction proper, affecting
the isolation level and the scope of that change. In response to a
mailing list request by Steven Davis.
Modified:
trunk/examples/transaction.cpp
trunk/lib/transaction.cpp
trunk/lib/transaction.h
Modified: trunk/examples/transaction.cpp
URL:
http://svn.gna.org/viewcvs/mysqlpp/trunk/examples/transaction.cpp?rev=2511&r1=2510&r2=2511&view=diff
==============================================================================
--- trunk/examples/transaction.cpp (original)
+++ trunk/examples/transaction.cpp Thu Apr 30 04:23:52 2009
@@ -1,6 +1,6 @@
/***********************************************************************
- transaction.cpp - Example showing how to use the transaction support in
- MySQL++ v2.1 and up.
+ transaction.cpp - Example showing how to use MySQL++'s transaction
+ features.
Copyright (c) 1998 by Kevin Atkinson, (c) 1999-2001 by MySQL AB, and
(c) 2004-2009 by Educational Technology Resources, Inc. Others may
@@ -55,7 +55,15 @@
// Insert a few rows in a single transaction set
{
- mysqlpp::Transaction trans(con);
+ // Use a higher level of transaction isolation than
MySQL
+ // offers by default. This trades some speed for more
+ // predictable behavior. We've set it to affect all
+ // transactions started through this DB server
connection,
+ // so it affects the next block, too, even if we don't
+ // commit this one.
+ mysqlpp::Transaction trans(con,
+ mysqlpp::Transaction::serializable,
+ mysqlpp::Transaction::session);
stock row("Sauerkraut", 42, 1.2, 0.75,
mysqlpp::sql_date("2006-03-06"),
mysqlpp::null);
@@ -74,6 +82,8 @@
// Now let's test auto-rollback
{
+ // Start a new transaction, keeping the same isolation
level
+ // we set above, since it was set to affect the session.
mysqlpp::Transaction trans(con);
cout << "\nNow adding catsup to the database..." <<
endl;
Modified: trunk/lib/transaction.cpp
URL:
http://svn.gna.org/viewcvs/mysqlpp/trunk/lib/transaction.cpp?rev=2511&r1=2510&r2=2511&view=diff
==============================================================================
--- trunk/lib/transaction.cpp (original)
+++ trunk/lib/transaction.cpp Thu Apr 30 04:23:52 2009
@@ -35,7 +35,7 @@
using namespace mysqlpp;
-//// ctor //////////////////////////////////////////////////////////////
+//// ctors /////////////////////////////////////////////////////////////
Transaction::Transaction(Connection& conn, bool consistent) :
conn_(conn),
@@ -43,6 +43,37 @@
{
// Begin the transaction set
Query q(conn_.query("START TRANSACTION"));
+ if (consistent) {
+ q << " WITH CONSISTENT SNAPSHOT";
+ }
+ q.execute();
+
+ // Setup succeeded, so mark our transaction as not-finished.
+ finished_ = false;
+}
+
+Transaction::Transaction(Connection& conn, IsolationLevel level,
+ IsolationScope scope, bool consistent) :
+conn_(conn),
+finished_(true) // don't bother rolling it back if ctor fails
+{
+ // Set the transaction isolation level and scope as the user wishes
+ Query q(conn_.query("SET "));
+ if (scope == session) q << "SESSION ";
+ if (scope == global) q << "GLOBAL ";
+ q << "TRANSACTION ISOLATION LEVEL ";
+ switch (level) {
+ case read_uncommitted: q << "READ UNCOMMITTED";
+ case read_committed: q << "READ COMMITTED";
+ case repeatable_read: q << "REPEATABLE READ";
+ case serializable: q << "SERIALIZABLE";
+ }
+ q.execute();
+
+ // Begin the transaction set. Note that the above isn't part of
+ // the transaction, on purpose, so that scope == transaction affects
+ // *this* transaction, not the next one.
+ q << "START TRANSACTION";
if (consistent) {
q << " WITH CONSISTENT SNAPSHOT";
}
Modified: trunk/lib/transaction.h
URL:
http://svn.gna.org/viewcvs/mysqlpp/trunk/lib/transaction.h?rev=2511&r1=2510&r2=2511&view=diff
==============================================================================
--- trunk/lib/transaction.h (original)
+++ trunk/lib/transaction.h Thu Apr 30 04:23:52 2009
@@ -46,13 +46,50 @@
class MYSQLPP_EXPORT Transaction
{
public:
- /// \brief Constructor
+ /// \brief Transaction isolation levels defined in SQL
+ ///
+ /// These values can be passed to one of the Transaction
+ /// constructors to change the way the database engine protects
+ /// transactions from other DB updates. These values are in order
+ /// of increasing isolation, but decreasing performance.
+ enum IsolationLevel {
+ read_uncommitted, ///< allow "dirty reads" from other
transactions
+ read_committed, ///< only read rows committed by other
transactions
+ repeatable_read, ///< other transactions do not affect
repeated reads in this transaction
+ serializable ///< this transaction prevents writes
to any rows it accesses while it runs
+ };
+
+ /// \brief Isolation level scopes defined in SQL
+ ///
+ /// These values are only used with one of the Transaction
+ /// constructors, to select which transaction(s) our change to
+ // the isolation scope will affect.
+ enum IsolationScope {
+ this_transaction, ///< change level for this transaction
only
+ session, ///< change level for all
transactions in this session
+ global ///< change level for all
transactions on the DB server
+ };
+
+ /// \brief Simple constructor
///
/// \param conn The connection we use to manage the transaction set
/// \param consistent Whether to use "consistent snapshots" during
/// the transaction. See the documentation for "START TRANSACTION"
/// in the MySQL manual for more on this.
Transaction(Connection& conn, bool consistent = false);
+
+ /// \brief Constructor allowing custom transaction isolation level
+ /// and scope
+ ///
+ /// \param conn The connection we use to manage the transaction set
+ /// \param level Isolation level to use for this transaction
+ /// \param scope Selects the scope of the isolation level change
+ /// \param consistent Whether to use "consistent snapshots" during
+ /// the transaction. See the documentation for "START TRANSACTION"
+ /// in the MySQL manual for more on this.
+ Transaction(Connection& conn, IsolationLevel level,
+ IsolationScope scope = this_transaction,
+ bool consistent = false);
/// \brief Destructor
///
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