Resource busy time out oracle message - Concurrency and Locks

Question

I have a requirement to generate gapless invoice and receipt number in our application. so i have currently used the below approach.
a. created table with a column to hold the invoice and receipt number sequence value.
b. whenever transaction gets succeed. i will lock the table which holds the invoice number and receipt number inorder to avoid the sequential number slipages.
Issue
1. since the application belongs to online payment through portal by customers, when concurrent users trying to pay and while generating receipt number's, i am facing with "resource busy time out" message frequently. Here i noticed when user1 locks the table to access the receipt number value and session is not committed or rollback and another session user2 trying to access the same resource, in this scenario i am facing this error.
Frequency of encountering this error is low, but customer was telling us this error is show stopper and affects normal business.
Is there any alternative solution or method can be applied to overcome this problem?
Current SQL used in application
cursor <cursor name> is.
select <column_name>
into <variable>
from <table name>
for update of wait 5
update <table name> set <column name> = value + 1
where current of <cursor name>

Answer 1

1e0ea4a1-1610-4dec-a44c-4ee1f46ba1a4 wrote:
I have a requirement to generate gapless invoice and receipt number in our application. so i have currently used the below approach.
Engage the business and inquire WHY this "requirement" exists. I have personally never seen an audit requirement wherein invoices MUST be devoid of gaps (that's not to say they do not exist, just that I've never seen one
They certainly must be unique, but that's what a sequence will do for you. If the business absolutely needs gapless information, then they will have to be willing to pay the price which is going to be longer transaction times (as requests queue in a busy system to get this sought after gapless resource). Your job is to explain this to them ... nothing comes without a cost.
The only thing you can really do (assuming you engage the business and the requirement doesn't change) is ensure the transactions are designed in such a manner that
1) they complete as fast as possible AND that the locking is done at the latest possible stage of the transaction
2) there is no user interaction (you cannot allow the users a "review" screen of any sort ... because users get silly sometimes and go for a coffee while reviewing things)
Cheers,