How long you can consider a pending transaction as invalid?

Question

I saw here that the time that a transaction can be at pending status changed, but didn't say how much

Due to overwhelming amounts of pending transactions during ICOs, many public nodes (etherscan, MEW, infura) adjusted their settings in order to keep more transactions in a pending state for a longer period of time.

Currently I'm studying relations in pending transactions over Ethereum blockchain, so I'd like to know how much time I can stop searching for a pending transaction, as it may cause ripple in my database, since new transactions with same data can happen.

Answer 1

There is no set limit. Every node can have its own limit, and the limit tends to depend on how many transactions there are in the pool. There isn't a way to know how long a transaction can be considered pending. A transaction could be mined years later assuming the nonce hadn't been used.