32K Columns

Oracle 12c has increased the maximum length of character-based columns to 32K bytes – don’t get too excited, they’re stored out of lines (so similar in cost to LOBs) and need some modification to the parameter file and data dictionary (starting the database in upgrade mode) before you can use them.

Richard Foote has a pair of articles on indexing such columns:

• Part 1
• Part 2

Be cautious about enabling this option and test carefully – there are going to be a number of side effects, and some of them may require a significant investment in time to resolve. The first one that came to my mind was that if you’ve created a function-based index on a pl/sql function that returns a varchar2() type and haven’t explicitly created the index on a substr() of the return value then the data type of the function’s return value will change from the current default of varchar2(4000) to varchar2(32767) – which means the index will become invalid and can’t be rebuilt or recreated.

Obviously you can redefine the index to include an explicit substr() call – but then you have to find all the code that was supposed to use the index and modify it accordingly.

Related posts:

1. Dynamic number of columns
2. Exchange Partition, Virtual Columns And Column Statistics
3. Exchange Partition, Virtual Columns And Column Statistics
4. (UTL_RAW.)CAST_TO_DATE
5. 12c Determinism
6. Date Columns at the end of Indexes
7. Date Columns at the end of Indexes
8. Undocumented Oracle Functions
9. FBI decode
10. Undocumented Oracle Functions