Same test as SERVER-36294 - 10 threads doing simple udpates to single independent documents.

At A 6 of the 10 threads got a TransientTransactionError, apparently (based on timing in chart above) because the in-progress transaction reaper job prevented them from acquiring a lock within 5ms:

Error: command failed: {
	"errorLabels" : [
		"TransientTransactionError"
	],
	"operationTime" : Timestamp(1532607909, 727),
	"ok" : 0,
	"errmsg" : "Unable to acquire lock '{6237343057549539649: Database, 1625657039122151745}' within a max lock request timeout of '5ms' milliseconds.",
	"code" : 24,
	"codeName" : "LockTimeout",
	"$clusterTime" : {
		"clusterTime" : Timestamp(1532607909, 727),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}

The 10 threads continue, but the open and active counters are now stuck ranging from 6-16 instead of 0-10. Apparently the counters have not been decremented on the error.

At B I killed the mongo shell. It appears there was still one transaction open at that point because open is 7 and inactive is 1. At C after that transaction times out we remain stuck indefinitely with open at 6 and active at 6.