Impala Memory limit exceed

hi there,

I have encountered a common error as follows:

Memory left in process limit: 180.41 GB
Memory left in query limit: -467.80 KB
Query(7e4794a439e5f26d:748d4c7c00000000): memory limit exceeded. Limit=1.00 GB Reservation=635.75 MB ReservationLimit=819.20 MB OtherMemory=388.71 MB Total=1.00 GB Peak=1.00 GB

I don't quite understand the difference between the "process limit" and "query limit", and what's the reservation memory for?

many thanks!