Tag Archives: commit

On implicit commit

An explicit commit is when you issue a COMMIT statement

SQL> create table t(x number);

Table created.

SQL> insert into t values(1);

1 row created.

SQL> commit;

Commit complete.

An implicit commit is when a commit is issued without your approval.

ex: AUTOCOMMIT (default is OFF)

SQL> set autoc on
SQL> insert into t values(1);

1 row created.

Commit complete.

ex: EXITCOMMIT (default is ON)

SQL> set autoc off exitc on
SQL> truncate table t;

Table truncated.

SQL> insert into t values(1);

1 row created.

SQL> disc
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> conn scott/tiger
Connected.
SQL> select * from t;
         X
----------
         1

before / after a successful DDL statement

SQL> truncate table t;

Table truncated.

SQL> insert into t values(1);

1 row created.

SQL> create index i on t(x);

Index created.

SQL> rollback;

Rollback complete.

SQL> select * from t;
         X
----------
         1

Before / after an unsuccessful DDL statement, sometimes :

SQL> truncate table t;

Table truncated.

SQL> insert into t values(1);

1 row created.

SQL> create index i on t(blabla);
create index i on t(blabla)
                    *
ERROR at line 1:
ORA-00904: "BLABLA": invalid identifier

SQL> rollback;

Rollback complete.

SQL> select * from t;
         X
----------
         1

But not always :

SQL> truncate table t;

Table truncated.

SQL> insert into t values(1);

1 row created.

SQL> create index i on t();
create index i on t()
                    *
ERROR at line 1:
ORA-00936: missing expression

SQL> rollback;

Rollback complete.

SQL> select * from t;

no rows selected

In the last case, no DDL was executed, but in the case before that, the DDL was executed and failed.

If you want to commit, use COMMIT :)

committing transaction

When and how do you commit a transaction?

SQL> insert into lsc_t(x) values(1);         ... (1) not committed
SQL> commit;                                 ... (1) committed

SQL> insert into lsc_t(x) values(2);         ... (2) not committed
SQL> alter table lsc_t disable primary key;  ... (2) committed

SQL> set autocommit ON
SQL> insert into lsc_t(x) values(3);         ... (3) committed
SQL> set autocommit OFF

SQL> insert into lsc_t(x) values(4);         ... (4) not committed
SQL> disc                                    ... (4) committed

Row 1 is committed after the commit keyword.

Row 2 is implicitely committed after before the alter table ddl statement.

Row 3 is autocommitted. Autocommit exists in sqlplus, but is more often seen in stateless applications (for instance a web application).

Row 4 is committed after a successfull disconnection.

But what appends if you kill your current session?


SQL> insert into lsc_t(x) values (5);

1 row created.

SQL> !ps
   PID TTY      TIME CMD
 13903 pts/33   0:00 ksh
 22384 pts/33   0:00 sqlplus

SQL> !kill 22384
Terminated

The row 5 is not commited

Ref: Overview of Transaction Management

A transaction ends when any of the following occurs:
- A user issues a COMMIT or ROLLBACK statement without a SAVEPOINT clause.
- A user runs a DDL statement such as CREATE, DROP, RENAME, or ALTER (*).
If the current transaction contains any DML statements, Oracle Database
first commits the transaction, and then runs and commits the DDL statement
as a new, single statement transaction.
- A user disconnects from Oracle Database. The current transaction is committed.
- A user process terminates abnormally. The current transaction is rolled back.

(*) but not ALTER SESSION

Please read On Implicit Commit