Transactions Internal implementation write ahead log and locks with banking examples 

Same 😅

LMAO

Well, he does a great come back from there :)

lol

Work in progress

@@TechDummiesNarendraL Would like to give one more suggestion if you allow. we should talk about qps estimation, memory/storage estimation, server estimation etc before jumping to arch of any system design question. Because this is how we should approach the problem. This helps us to decide 1. Database load 2. Servers and load balancer technique 3. how the system is resilient

Wallets are not always individually maintained. Couples often have shared wallets, as do departments in a company for members of the department to expense items.

It sounds fine to me. Maybe there's a problem with your speakers?

Yes ,exactly what I am thinking in case there is a C user who want to send money to A.Then lock will be on C. And A will have wrong amount.

That's not how it works . for a transfer there are 3 operations 1. withdraw() -> acquire lock on A 2. Deposit() -> Acquire lock on B 3. deduct_commission() -> Acquire lock on A A transaction is said to be successful if and only if all of 3 steps are successful. else it will fall under redo() or abort() there are different strategies followed by different Database system. one of them is acquiring all the required locks before transaction starts. another is request for lock if required. both the strategies have it's own pros and cons and deadlock situations. which is also taken into account when designing a lock mechanism. Hope this helps

purpose served :)