Level 67
Sure, just the same as if it was a single app with no load balancer and 2 requests came in at the same time altering the same record.
Jun 19, 2018
8
Level 8
Scaling app
Hello guys, i have one interesting question. If i have 3 instances of my application with load balancer, can be the situation when 2 instance edit some info in the database at the same time? (Race condition as i remember correctly). Anybody know about this something?
Level 8
But if we write code correctly, we will not have race condition with one application instance. But if we have 2 or more app instance that connect to 1 database, we have a risk with this. Did you have this problem when using several app instance?
Level 8
No means that you haven't this problem or you are using pessimistic-locking with all your db query?)
Level 67
I don't have the problem bc of of the locking
Level 8
Maybe pessimistic-locking must be used for shared data, that can be modify by several users at the same time i think, but i'm not sure.
Level 67
Yes, just as you said here, which I thought was what you're trying to resolve? Locking the table resolves that.
when 2 instance edit some info in the database at the same time
But whether it's 500 app servers behind a load balancer all using a common database, or a single server using a single database, the problem is the same. The problem is "2 or more requests to edit the same record in the same database at the same time." Where the requests actually come from don't matter. It could be multiple servers, or the same server.
Level 75
If i have 3 instances of my application with load balancer
No you only have one, let the (if properly set up) load balancer do it's job, not even something to be concerned about.
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