Problem

Under 2.8.0-rc2 with WT storage engine there are a few mongo-perf tests that show further optimization could be consider, when considered against mmapv1.

Update.MmsIncShallow1
Update.MmsIncShallow2
Update.MmsIncDeep1
Update.MmsIncDeepSharedPath2
Update.MmsIncDeepSharedPath3
Update.MmsIncDeepDistinctPath2
Update.MmsIncDeepDistinctPath3
Update.FieldAtOffset

Each of these tests is a single contended document, with 512k fields, where one field is being updated.

Reproduce

python ./benchrun.py -f testcases/*.js --trialTime 5 --trialCount 1 -l mytest --nodyno --testFilter "['Update.MmsIncShallow1']" -m 1 -c 1 -t 12