トランザクション分離の Java の例

トランザクション分離は、1 つの操作で行われた変更がどのように他の並行操作に可視になるのかを定義します。以下の例を使用して、Java™ アプリケーションでトランザクション分離レベルを定義できます。

ペシミスティック・ロックでの反復可能読み取り

map = session.getMap("Order");
session.setTransactionIsolation(Session.TRANSACTION_REPEATABLE_READ);
session.begin();

// An S lock is requested and held and the value is copied into 
// the transactional cache.
Order order = (Order) map.get("100");
// The entry is evicted from the transactional cache.
map.invalidate("100", false);

// The same value is requested again.  It already holds the 
// lock, so the same value is retrieved and copied into the 
// transactional cache.
Order order2 = (Order) map.get("100");

// All locks are released after the transaction is synchronized
// with cache map.
session.commit();

幻償読み取り

session1.setTransactionIsolation(Session.TRANSACTION_REPEATABLE_READ);
session1.begin();

// A query is run which selects a range of values.
ObjectQuery query = session1.createObjectQuery
    ("SELECT o FROM Order o WHERE o.itemName='Widget'");

// In this case, only one order matches the query filter.  
// The order has a key of "100".
// The query engine automatically acquires an S lock for Order "100".
Iterator result = query.getResultIterator();

// A second transaction inserts an order that also matches the query.
Map orderMap = session2.getMap("Order");
orderMap.insert("101", new Order("101", "Widget"));

// When the query runs again in the current transaction, the 
// new order is visible and will return both Orders "100" and "101".
result = query.getResultIterator();

// All locks are released after the transaction is synchronized
// with cache map.
session.commit();

ペシミスティック・ロックでの読み取りコミット済み

map1 = session1.getMap("Order");
session1.setTransactionIsolation(Session.TRANSACTION_READ_COMMITTED);
session1.begin();

// An S lock is requested but immediately released and
//the value is copied into the transactional cache.

Order order = (Order) map1.get("100");

// The entry is evicted from the transactional cache.
map1.invalidate("100", false);

// A second transaction updates the same order.
// It acquires a U lock, updates the value, and commits.
// The ObjectGrid successfully acquires the X lock during
// commit since the first transaction is using read
// committed isolation.

Map orderMap2 = session2.getMap("Order");
session2.begin();
order2 = (Order) orderMap2.getForUpdate("100");
order2.quantity=2;
orderMap2.update("100", order2);
session2.commit();

// The same value is requested again.  This time, they
// want to update the value, but it now reflects
// the new value
Order order1Copy = (Order) map1.getForUpdate("100");