Oracle 11g JDBC prefetching keys

Question

My app needs to know which row receives which key in the database.

I am using JDBC on read commited isolation level with batch updates. Therefore retrieving the keys with getGeneratedKeys isn't possible. My plan is to fetch a Range of ids from the database in a transaction safe way, eg two parallel transactions can't get the same keys.

Can I write some SQL-Query with the number of future rows as an argument to fetch a list of future keys in Oracle 11g?

What are my options here?

Answer 1

you can use sequences for this purpose:

create sequence s;

to retrieve a id

select s.nextval from dual;

or to retrieve a range of ids :

select s.nextval from dual connect by level <= 10;

Answer 2

Just wanted to add:

There is no explicit relationship between sequences and tables. A sequence is simply a mechanism for generating numerical sequences. You can assume that a sequence will never produce a duplicate value, and that's about it. Don't assume order, and definitely don't expect a gap-free sequence. Sequences are done this way in Oracle, by design. By following those rules, and making no other assumptions about a sequence's behavior, we get extremely scalable performance with sequences. Note that as soon as you try to enforce an order or a gap-free sequence, your performance suffers severely.

In summary: 1.) Sequences are dead simple, and really fast. 2.) Other than "no dups", don't assume you can predict a sequence's behavior. 3.) Sequences are independent objects, not tied to a table, and can be used to generate sequence values that will be used in the same table, or many different tables.

Hope that helps.