The automated performance testing on Windows has shown a performance change correlated with a recent update of WiredTiger into MongoDB master branch.

The job showing the change is:
http://build.wiredtiger.com:8080/job/mongodb-perf-ycsb-windows

The particular build that triggered the change is:
http://build.wiredtiger.com:8080/job/mongodb-perf-ycsb-windows/975/

Which included https://github.com/mongodb/mongo/commit/c91b93d2786342505fd9e151c8aa6b68ee03a1fb for the first time.

It was the small documents job that shows a regression, the standard and large document workloads don't show a performance change. All small document runs are slower.

The 80r/20u job had a throughput of ~35k ops/sec up to build 972, builds 973 and 974 throughput was ~30k ops/sec, from build 975 throughput fell to 12.5k ops/sec.