db.adminCommand({ setParameter: 1, internalQueryCBRCEMode: "samplingCE" , internalQueryPlanRanker: "costBased" , internalQueryStatsSampleRate: 1 }); db.a.drop(); db.a.insertOne({}); db.a.createIndex({ a: 1 }); db.a.createIndex({ b: 1 }); db.adminCommand({setParameter: 1, internalQueryStatsCacheSize: "0MB" }) // drop all the existing entries db.adminCommand({setParameter: 1, internalQueryStatsCacheSize: "1%" }) // restore the default db.a.find({ a: 0, b: 0 }).toArray(); printjson(db.getSiblingDB( "admin" ).aggregate([ { $queryStats: {} }, { $match: { "key.queryShape.cmdNs.coll" : "a" } }, { $project: { key: 1, cbr: "$metrics.queryPlanner.costBasedRanker" } }, ]).toArray());   Gives: ... nDocsSampled: { sum: Long('384'), max: Long('384'), min: Long('384'), sumOfSquares: Decimal128('147456') } Even though we don't actually sample more documents than there are in the collection (only 1 in this case). For reference, the commit right before SERVER-130972 returns the correct numbers:         nDocsSampled: {         sum: Long('1'),         max: Long('1'),         min: Long('1'),         sumOfSquares: Decimal128('1')       }