What does it mean that the next DAG is in X days?
Before you jump all over this a duplicate question. I did read things related to DAG like here: What actually is a DAG? But that doesn't answer my question, what does it mean when my mining pool website says that the next DAG is in X (4 in my case) days? How does that affect me as a miner?
Every miner need to download DAG file ?both of solo miner and pool miners ? has any effect to hash rate power of graphic card in pool mining ?if yes which model is better ?
I usually avoid copy pasting info from docs, as many here do, but here I think its appropriate:
Ethash uses a DAG (directed acyclic graph) for the proof of work algorithm, this is generated for each epoch, i.e every 30000 blocks (100 hours). The DAG takes a long time to generate. If clients only generate it on demand, you may see a long wait at each epoch transition before the first block of the new epoch is found. However, the DAG only depends on block number, so it CAN and SHOULD be calculated in advance to avoid long wait at each epoch transition. geth implements automatic DAG generation and maintains two DAGS at a time for smooth epoch transitions. Automatic DAG generation is turned on and off when mining is controlled from the console. It is also turned on by default if geth is launched with the --mine option. Note that clients share a DAG resource, so if you are running multiple instances of any client, make sure automatic dag generation is switched on in at most one client. Note that ethash uses ~/.ethash (Mac/Linux) or ~/AppData/Ethash (Windows) for the DAG so that it can shared between clients.
So this *still* doesn't quite answer the question: how does it affect miners? Obviously most miners asking this question haven't chosen whether or not they have "Automatic DAG generation" switched on or off... Are you saying we should switch it on? Is it on by default?
I think the answers to your questions are in the cited text: Are you saying we should switch it on? "the DAG only depends on block number, so it CAN and SHOULD be calculated in advance to avoid long wait at each epoch transition" Is it on by default? "It is also turned on by default if geth is launched with the --mine option"