public class Transactions {
public static void main(String[] args) {
//Open Transaction Factory. DBMaker shares most options with single-transaction mode.
TxMaker txMaker = DBMaker
.newMemoryDB()
.makeTxMaker();
// Now open first transaction and get map from first transaction
DB tx1 = txMaker.makeTx();
//create map from first transactions and fill it with data
Map map1 = tx1.getTreeMap("testMap");
for(int i=0;i<1e4;i++){
map1.put(i,"aaa"+i);
}
//commit first transaction
tx1.commit();
// !! IMPORTANT !!
// !! DB transaction can be used only once,
// !! it throws an 'already closed' exception after it was commited/rolledback
// !! IMPORTANT !!
//map1.put(1111,"dqdqwd"); // this will fail
//open second transaction
DB tx2 = txMaker.makeTx();
Map map2 = tx2.getTreeMap("testMap");
//open third transaction
DB tx3 = txMaker.makeTx();
Map map3 = tx3.getTreeMap("testMap");
//put some stuff into second transactions, observer third map size
System.out.println("map3 size before insert: "+map3.size());
map2.put(-10, "exists");
System.out.println("map3 size after insert: "+map3.size());
//put some stuff into third transactions, observer second map size
System.out.println("map2 size before insert: "+map2.size());
map3.put(100000, "exists");
System.out.println("map2 size after insert: "+map2.size());
// so far there was no conflict, since modified Map values lie far away from each other in tree.
// `map2` has new key -10, so inserting -11 into map3 should update the same node
map3.put(-11, "exists");
// `map2` and `map3` now have conflicting data
tx3.commit();
System.out.println("Insert -11 into map3 was fine");
//tx3 was commited, but tx2 now has conflicting data, so its commit will fail
try{
tx2.commit();
throw new Error("Should not be here");
}catch(TxRollbackException e){
System.out.println("Tx2 commit failed thanks to conflict, tx2 was rolled back");
}
//create yet another transaction and observe result
DB tx4 = txMaker.makeTx();
Map map4 = tx4.getTreeMap("testMap");
System.out.println("Map size after commits: "+map4.size());
System.out.println("Value inserted into tx2 and successfully commited: "+map4.get(-10));
System.out.println("Value inserted into tx3 before rollback: "+map4.get(100000));
System.out.println("Value inserted into tx3 which triggered rollback: "+map4.get(-11));
//close transaction without modifying anything
tx4.close();
//close the entire database
txMaker.close();
}