Are you seeing the same error, if you reduce the number of workers?
If not, then it could point to an insufficient amount of shared memory. Could you check, how much shared memory your system is using at the moment?



 rui_zhang_331:

Also I wonder what is really shared memory used in multi worker data loader case


Each workers is a process, which needs to communicate with the main process e.g. via shared memory. Multi-threading is not really an option in Python due to the GIL.