Updating millions of records in oracle
Updating millions of records in oracle - Free online sexchat without credit card
This is especially important for high update tables with more than 100 row changes per second."The most common issue with updates is the requirement to have a complex SELECT statement is the where clause to identify the rows to be updated.
If you’ve been around the Oracle community for some time you’ve probably realized, either through your own experience or by reading articles, if you are able to accomplish a task using a single SQL statement then that is preferred over using PL/SQL and SQL both are incredibly powerful languages that allow us to do some pretty amazing things with data.
For example, assume that the following update changed 75% of the table rows: shows a case where the developer forgot to include the SET condition in the UPDATE WHERE clause, causing high redo waits (log file parallel write waits, log file sync waits).
Simply including the existing state of the SET clause can result in a huger performance improvement for UPDATE statements: As more people adopt 64-bit servers with giant data buffers, we see a delay caused by the database writer process having to scan through giant data buffers seeking dirty blocks.
The following table summarizes the average of 10 executions of each of the UPDATE statements, the MERGE statement, and the PL/SQL block.
The results are rather interesting: The PL/SQL block out-performed both of the updates and was nearly on par with the MERGE statement, even in an ideal world. I think it is a reminder that we should be both aware of and willing to explore all of our options as developers.
Would it be faster to create a new table rather then update it?
Would it be better to create a loop and update 100000 records each time and commit after each iteration?
You can use a DECODE statement: Please note that 1,2,3 and a,b,c,.. It would also be great if you can send the approximate performance numbers expected.
would it be 1 min, 10 min, 1 hour etc for the above scenario.
COUNT 25 UPDATE employees 26 SET employee_salary = lt_new_salary_info(i).new_salary 27 WHERE employee_id = lt_new_salary_info(i).employee_id; 28 29 v_rowcount := v_rowcount SQL%ROWCOUNT; 30 END LOOP; 31 32 CLOSE c_new_salary_info; 33 34 DBMS_OUTPUT. The first reason has already been noted, and that is the use of bulk operations and FORALL to reduce context switching between PL/SQL and SQL. The optimizer no longer has to worry about performing an update as part of the query and is able to simply join the two tables in a very efficient manner.