MongoDB - explain execution plan

Please indicate the source for reprinting: https://blog.csdn.net/l1028386804/article/details/80003204

MongoDB provides an explain command to let us know how the system handles query requests. Using the explain command, we can get a good look at how the system uses the index to speed up retrieval, and we can optimize the index accordingly.

> db.t5.ensureIndex({name:1})
> db.t5.ensureIndex({age:1})
> db.t5.find({age:{$gt:45}}, {name:1}).explain()
{
	"cursor" : "BtreeCursor age_1",
	"nscanned" : 0,
	"nscannedObjects" : 0,
	"n" : 0,
	"millis" : 0,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"isMultiKey" : false,
	"indexOnly" : false,
	"indexBounds" : {
		"age" : [
			[
				45,
				1.7976931348623157e+308
			]
		]
	}
}

Field Description:

• cursor: Returns the cursor type (BasicCursor or BtreeCursor)
• nscanned: the number of documents scanned
• n: number of documents returned
• millis: time (milliseconds)
• indexBounds: the index to use