Himanshu Sharma

我们可以利用 facet 在数据上运行并行管道,然后合并每个管道的输出。

db[source].aggregate([
    {
        $match: { 
            date: {
                $gt: minDate, // Filter out by time frame...
                $lt: maxDate
            }
        }
    },
    {
        $match: { 
            [filterTarget]: searchTerm // Match search query....
        }
    },
    {
        $set: {
            [filterTarget]: { $toLower: `$${filterTarget}` } // Necessary to ensure that sort works properly...
        }
    },
    {
        $sort: {
            [sortBy]: sortOrder // Sort by date...
        }
    },
    {
        $facet:{
            "data":[
                {
                    $skip: skip
                },  
                {
                    $limit:rowsPerPage
                }
            ],
            "info":[
                {
                    $count:"count"
                }
            ]
        }
    },
    {
        $project:{
            "_id":0,
            "data":1,
            "count":{
                $let:{
                    "vars":{
                        "elem":{
                            $arrayElemAt:["$info",0]
                        }
                    },
                    "in":{
                        $trunc:"$$elem.count"
                    }
                }
            }
        }
    }
]).pretty()

可以在文件本身中指定开始时间和结束时间。下面是一个例子:

var start_time = new Date().valueOf();
db.telephone.find({'brand' : 'Apple'});
db.telephone.find({'brand' : 'Samsung'});
var end_time = new Date().valueOf();
print(end_time-start_time);

我们如何精确地测量执行时间?

要分析查询,可以使用 explain() . 它返回查询的完整统计信息。下面是一个例子:

db.telephone.find({'brand' : 'Apple'}).explain("executionStats")

输出:

{
    "queryPlanner" : {
        "plannerVersion" : 1,
        "namespace" : "check.telephone",
        "indexFilterSet" : false,
        "parsedQuery" : {
            "brand" : {
                "$eq" : "Apple"
            }
        },
        "winningPlan" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "brand" : {
                    "$eq" : "Apple"
                }
            },
            "direction" : "forward"
        },
        "rejectedPlans" : [ ]
    },
    "executionStats" : {
        "executionSuccess" : true,
        "nReturned" : 1,
        "executionTimeMillis" : 35,
        "totalKeysExamined" : 0,
        "totalDocsExamined" : 1,
        "executionStages" : {
            "stage" : "COLLSCAN",
            "filter" : {
                "brand" : {
                    "$eq" : "Apple"
                }
            },
            "nReturned" : 1,
            "executionTimeMillisEstimate" : 0,
            "works" : 3,
            "advanced" : 1,
            "needTime" : 1,
            "needYield" : 0,
            "saveState" : 0,
            "restoreState" : 0,
            "isEOF" : 1,
            "invalidates" : 0,
            "direction" : "forward",
            "docsExamined" : 1
        }
    },
    "serverInfo" : {
        "host" : "theMechanic",
        "port" : 27017,
        "version" : "4.0.11",
        "gitVersion" : "417d1a712e9f040d54beca8e4943edce218e9a8c"
    },
    "ok" : 1
}

注: 这个 executionStats.executionTimeMillis 保留实际查询执行时间。