database - Reserve sequence range in DB2 -

we moving application oracle db2. batch job. there sequencing logic assigns ids entries before processing:

1. reserve range of sequences

   select my_sequence.nextval; // range_start;

   alter sequence my_sequence increment range_size;

   select my_sequence.nextval;

   alter sequence my_sequence increment 1;

   select my_sequence.nextval; // range_end;

2. assign ids within range via in-memory incremented value:

   for id = range_start:range_end do

this worked fine in oracle, gave unexpected results in db2.

in oracle:

drop sequence my_sequence; create sequence  my_sequence minvalue 1 maxvalue 999999999999999999999999999 increment 1 start 1 cache 50000 noorder  nocycle ; select my_sequence.nextval dual; // 1; select my_sequence.nextval dual; // 2; alter sequence my_sequence increment 100000; select my_sequence.nextval dual; // 100002; alter sequence my_sequence increment 1; select my_sequence.nextval dual; // 100003; 

in db2:

drop sequence my_sequence; create sequence my_sequence decimal(27 , 0)  start 1 increment 1 minvalue 1 maxvalue 999999999999999999999999999 no cycle cache 50000 no order;  select my_sequence.nextval dual; // 1; select my_sequence.nextval dual; // 2; alter sequence my_sequence increment 100000; select my_sequence.nextval dual; // 150000; alter sequence my_sequence increment 1; select my_sequence.nextval dual; // 5000050001; 

i think 150000 may explained cache size. have no idea yet 5000050001 value. here highly appreciated.

notes:

• im aware of alter statements being non-transactional. process have exclusive access db time launched , runs non-distributed , single-threaded.
• db2 runs in ora compatibility mode
• the same issue in db2 appears if db2 sequence next val used: values next value my_sequence;
• same issue ordered sequences

altering sequence no cache fixed issue.