performance drops significantly when writing 10,000 variables using adios2 bp engine at each step

Created by: lwan86

I was testing the miniapp code under my branch https://github.com/lwan86/ADIOS2-Examples/tree/miniapp. When writing 10,000 variables at each step, using adios2 bp engine suffers from significant performance degradation compared to using adios1 engine.

This issue can be reproduced on both ubuntu VMs and macbook laptops.