Oracle sequence generator within interval

Question

I'm using oracle 11gr2 and for the product table when a new product is inserted I need to assign an autoincrement id going from 1 to 65535. Product could be then be deleted. When I reach the 65535th, I need to scan the table to find a free hole for assigning new ID. As I have this requirement oracle sequence could not be used, so I am using a function (tried also a trigger on insert) in order to generate a free id... The problem is that I could not handle batch insert for example and I have concurrency problems... How could I solve this ? By using some sort of external Id generator ?

Answer 1

Sounds like an arbitrary design. Is there a good reason for having a 16-bit max product id or for reusing IDs? Both constraints are bad practice.

I doubt any external generator is going to provide anything that Oracle doesn't already provide. I recommend using sequences for batch insert. The problem you have is how to recycle the IDs. Oracle plain sequences don't track the primary key, so you need a solution to find recycled keys first, then fallback to the sequence perhaps.

Product ID Recycling

1. Batch Inserts - Use sequence for keys the first time you load them. For this small range, set NOCACHE on the sequence to eliminate gaps.
2. Deletes - When a product is deleted, instead of actually deleting the row, set a DELETED = 'Y' flag on the row.
3. Inserts - Update the first record available with DELETED flag set, or either select the min ID from product table where DELETED = 'Y'. Update record with new product info (but same ID) and set DELETED = 'N'

This ensures you always recycle before you insert new sequence IDs

If you want to implement the logic in the database, you can create a view (VIEW$PRODUCTS) where DELETED = 'N' and an INSTEAD OF INSERT trigger to do the insert.

In any scenario, when you run out of sequences (or sequence wraps), you are out of luck for batch inserts. I'd reconsider that part of the design if I were you.