How to prefetch Oracle sequence ID-s in a distributed environment

Why not just have the sequence as increment by 100 all the time? each "nextval" gives you 100 sequence numbers to work with

SQL> create sequence so_test start with 100 increment by 100 nocache;

Sequence created.

SQL> select so_test.nextval - 99 as first_seq, so_test.currval as last_seq from dual;

 FIRST_SEQ   LAST_SEQ
---------- ----------
         1        100

SQL> /

 FIRST_SEQ   LAST_SEQ
---------- ----------
       101        200

SQL> /

 FIRST_SEQ   LAST_SEQ
---------- ----------
       201        300

SQL> 

A note on your example.. Watch out for DDL.. It will produce an implicit commit

Example of commit produced by DDL

SQL> select * from xx;

no rows selected

SQL> insert into xx values ('x');

1 row created.

SQL> alter sequence so_test increment by 100;

Sequence altered.

SQL> rollback;

Rollback complete.

SQL> select * from xx;

Y
-----
x

SQL> 

Why do you need to fetch the sequence IDs in the first place? In most cases you would insert into a table and return the ID.

insert into t (my_pk, my_data) values (mysequence.nextval, :the_data)
returning my_pk into :the_pk;

It sounds like you are trying to pre-optimize the processing.

If you REALLY need to pre-fetch the IDs then just call the sequence 100 times. The entire point of a sequence is that it manages the numbering. You're not supposed to assume that you can get 100 consecutive numbers.