Re: A Typical Concurrent Access Problem

let's say you have 1000 storage spaces in the warehouse, and the space number 1000 is always used. Your approach won't let you use spaces 1-999, correct? Probably your solution does not work.

I would

1. a table to serialize on

create table serializer(toggle number(1)); insert into serializer values(1);

2. have a table for storage spaces
create table storage(space_num number, used_by varchar2(50));
--- populate it

---reusing available space
--- 1. serialize

update serializer set toggle = 1 - toggle;
--- this acquires an update lock on the modified row

• other requests are waiting on the update lock

update storage set used_by='somebody' where space_num = (select min(space_num) into v_unused_num from storage where used_by is null);

commit;
--- update lock released, another request may proceed
Received on Thu Jun 09 2005 - 09:14:12 CDT