[Wellington-pm] Perl database stuff....

[Sam Vilain]

michael at diaspora.gen.nz wrote:

>     A: select 1 from table where business_key = ...; # off to database
>     if select returned nothing
>     begin
> 	B: select sequence.nextval into id; # off to database
> 	C: insert into table values (id, business_key); # off to database
>     end;
> 
> Between A and B, unless you wrap a lock around the operation, there's a
> race condition; you could find either C failing (if there's a uniqueness
> constraint on "business_key"), or duplicate values in "table" (if
> there isn't).

Surely just wrapping the entire operation in a transaction is enough?
Or is that one of those cases that needs the TRANSACTION ISOLATION LEVEL
set to max?

Sam.