Subject Re: [firebird-support] Re: Hundreds of Generators
Author Venus Software Operations
Ann, thanks for the pointer I will keep a check on the rdb$generator_id

As for missing numbers using generators. I have put in code in my app
framework which will bring a number from the generator without
incrementing it. At the time of saving if the number is still valid it
will bring that number from the generator again without incrementing. In
case of conflict, where some one (or more) have taken up numbers since
it was shown to the user, the user is then allowed to use the latest
number available or do nothing (essentially cancel) to the record. If no
conflict call the generator once again allowing it to update. But this
is all client side code.

Thanks for the code Ann. Is it possible to have a table that I can make
it work like generators by doing the manipulations I am doing above. I
just have to repointer my code to use this table instead?

Kind regards

On 29/04/2010 09:24 pm, Ann W. Harrison wrote:
> venussoftop wrote:
> > Thanks Ann, I will try gstat. Is there something stored in the
> database system tables that I can directly SQL-Pass-Through from my
> application?
> You don't really care how long it's been since a backup/restore.
> What you care about is the number of generators that have been
> issued, which will be the max value of rdb$generator_id in
> rdb$generators. If you check that weekly or monthly and if
> it's higher than 30,000, backup and restore the database.
> That doesn't solve the potential problem of lost numbers. If
> a transaction gets a value from a generator and rolls back or
> for some other reason doesn't use the value, that value is
> lost. There are lots of ways around the problem, some of which
> introduce the problem of numbers being assigned out of sequence.
> If your number sequence must be contiguous, and in order of
> assignment, and assigned to several concurrent users, generators
> will not work.
> This will work
> create table number_generator (
> thing_to_be_numbered varchar(50) not null,
> active_year integer not null,
> generated_number integer,
> primary key (thing_to_be_numbered, active_year));
> create procedure get_number
> (thing varchar(50), active_year integer)
> returns (generated_number integer)
> as begin
> select count(*) from number_generator
> where thing_to_be_numbered = :thing and
> active_year = :active_year
> into :generated_number;
> if (:generated_number = 0)
> then begin
> insert into number_generator
> (thing_to_be_numbered, active_year, generated_number)
> values (:thing, :active_year, 1);
> generated_number = 1;
> end
> else begin
> update number_generator
> set generated_number = generated_number + 1
> where thing_to_be_numbered = :thing and
> active_year = :active_year;
> select generated_number from number_generator
> where thing_to_be_numbered = :thing and
> active_year = :active_year
> into :generated_number;
> end
> suspend;
> end
> You'll get an error if two people try to run the procedure at
> the same time.


Thanking you.

Yours Faithfully,
For Venus Software Operations
Bhavbhuti Nathwani
Softwares for Indian Businesses at:


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