Mongodb write performance is confusing

Question

I did a write performance test in MongoDB using YCSB and it is producing the confusing result,

./bin/ycsb load mongodb -s -P workloads/workloada -p recordcount=10000 -threads $tread_count -p mongodb.url="mongodb://testuser:testpassword@12.18.56.14:27017/admin" -p mongodb.auth="true"

Consider the 10K write performance result with different threads (Execution in Parallel using YCSB) when the number of threads are increasing from 4 to 128, I expected the decrease in total time and increase in operations per second

But in 128 threads for 10K count, It shows a sudden increase in Total time and Decrease in Operations per second, Is it expected? If so could someone explain it please.

Thanks,
Harry

Answer 1

As the number of threads goes up, locking overhead and lock contention increase. Eventually adding more threads no longer improves performance.