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The most serious problem with the commit before the logical transaction is over approach is the fact that it frequently leaves your database in an unknown state if the UPDATE fails halfway through. Unless you planned for this ahead of time, it is very hard to restart the failed process, allowing it to pick up where it left off. For example, say we were not applying the LOWER() function to the column, as in the previous example, but rather some other function of the column, such as last_ddl_time = last_ddl_time + 1; If we halted the UPDATE loop partway through, how would we restart it We could not just rerun it, as we would end up adding 2 to some dates, and 1 to others. If we fail again, we would add 3 to some, 2 to others, 1 to the rest, and so on. We need yet more complex logic some way to partition the data. For example, we could process every OBJECT_NAME that starts with A, and then B, and so on: ops$tkyte%ORA11GR2> create table to_do 2 as 3 select distinct substr( object_name, 1,1 ) first_char 4 from T 5 / Table created. ops$tkyte%ORA11GR2> ops$tkyte%ORA11GR2> begin 2 for x in ( select * from to_do ) 3 loop 4 update t set last_ddl_time = last_ddl_time+1 5 where object_name like x.first_char || '%'; 6 7 dbms_output.put_line( sql%rowcount || ' rows updated' ); 8 delete from to_do where first_char = x.first_char; 9 10 commit; 11 end loop; 12 end; 13 / 1270 rows updated

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Now that we have established a connection to the database engine, we can explicitly create a database from F# code by executing a SQL statement directly. For example, you can create a database called company as follows: open System.Data open System.Data.SqlClient let execNonQuery conn s = let comm = new SqlCommand(s, conn, CommandTimeout = 10) comm.ExecuteNonQuery() |> ignore execNonQuery conn "CREATE DATABASE company" You will be using execNonQuery in the subsequent sections. This method takes a connection object and a SQL string and executes it as a SQL command, ignoring its result.

3122 rows updated 7 rows updated 5 rows updated 8 rows updated 2627 rows updated 16 rows updated 3 rows updated 11 rows updated 3 rows updated PL/SQL procedure successfully completed. Now, we could restart this process if it fails, since we would not process any object name that had already been processed successfully. The problem with this approach, however, is that unless we have some attribute that evenly partitions the data, we will end up having a very wide distribution of rows. The second UPDATE did more work than all of the others combined. Additionally, if other sessions are accessing this table and modifying the data, they might update the object_name field as well. Suppose that some other session updates the object named Z to be A, after we already processed the As. We would miss that record. Furthermore, this is a very inefficient process compared to UPDATE T SET LAST_DDL_TIME = LAST_DDL_TIME+1. We are probably using an index to read every row in the table, or we are full-scanning it n times, both of which are undesirable. There are so many bad things to be said about this approach.

DBMS_PARALLEL_EXECUTE package. There we ll revisit this restartable approach and deal with the non-uniform

Note If you try to create the same database twice, you will receive a runtime exception. However, if you do intend to drop an existing database, you can do so by issuing a DROP DATABASE company SQL command. The DROP command can also be used for other database artifacts, including tables, views, and stored procedures.

The best approach is the one I advocated at the beginning of 1 Developing Successful Oracle Applications : do it simply. If it can be done in SQL, do it in SQL. What can t be done in SQL, do in PL/SQL. Do it using the least amount of code you can. Have sufficient resources allocated. Always think about what happens in the event of an error. So many times, I ve seen people code update loops that worked great on the test data but then failed halfway through when applied to the real data. Then they are really stuck, as they have no idea where the loop stopped processing. It s a lot easier to size undo correctly than to write a restartable program. If you have truly large tables that need to be updated, you should be using partitions (more on that in 10 Database Tables ), which you can update each individually. You can even use parallel DML to perform the update, or in Oracle Database 11g Release 2 and above, the DBMS_PARALLEL_EXECUTE package.

My final words on bad transaction habits concern the one that arises from using the popular programming APIs ODBC and JDBC. These APIs autocommit by default. Consider the following statements, which transfer $1,000 from a checking account to a savings account: update accounts set balance = balance - 1000 where account_id = 123; update accounts set balance = balance + 1000 where account_id = 456;