alright. Thanks
So as a pool operator/developer one of the most important things is to make sure that every single miner connected to the pool gets different work. ?
Which is controlled by the nonce/extranonce each miner gets, right ?
For my understanding , nonce itself is to small for modern miners anyway and overflows under a second. So miner starts changeing extranonce, which is also just a number that will be incremented?
Question: How is guaranteed that every single miner realy does unique work. ? How is secured that each miner changes nonce and extranonce values differently to make sure no duplicated shares are created.
Stratum sends a different, incomplete coinbase transaction to each miner.
https://bitcointalksearch.org/topic/stratum-protocol-documentation-557866
Every pool will have a different coinbase for the simplest reason: no pool wants to send their block reward to another pool.
However, if the pool has 2 or more different work generators (i.e. 2 or more different work servers) they of course must ensure that the coinbase is different on them.
Each miner on the same pool gets a slightly different coinbase from the pool work generator.
If not, then the pool luck will drop - and no pool wants ... e.g. 50% luck coz they always send the same work to two different miners.