coll = db.foo;
coll.drop();

for (let i = 0; i < 1000; i++) {
     coll.insertMany([{a: i,b:1}]);
}

db.adminCommand({setParameter: 1, planRankerMode: "multiPlanning"});
db.runCommand({analyze: "foo", key: "a"});

db.adminCommand({setParameter: 1, planRankerMode: "histogramCE"});
db.foo.aggregate([{$match:{a: {$exists: false}}}]).explain();