Constant solana_sdk::clock::MAX_HASH_AGE_IN_SECONDS

pub const MAX_HASH_AGE_IN_SECONDS: usize = 120; // 120usize

The time window of recent block hash values that the bank will track the signatures of over. Once the bank discards a block hash, it will reject any transactions that use that recent_blockhash in a transaction. Lowering this value reduces memory consumption, but requires clients to update its recent_blockhash more frequently. Raising the value lengthens the time a client must wait to be certain a missing transaction will not be processed by the network.