Oh, ok.
So what are the allocated values for memory and cpu, and what are the values of GOMEMLIMIT and GOMAXPROCS?
Not sure you have read thru this nice blog article about GOMEMLIMIT:
Because you are using a flat index, your heap will not be an issue here, (you are storing on disk, not on memory), but setting those variables can force garbage collection kick in quicker and free up memory.
Let me know if that helps!
THanks!