db. コレクション.explain()（mongoshメソッド）

パラメーター

The db.collection.explain() method has the following parameter:

冗長モード

The behavior of db.collection.explain() and the amount of information returned depend on the verbosity mode.

Explain 操作と Write 操作

For write operations, db.collection.explain() returns information about the write operation that would be performed but does not actually modify the database.

制限事項

You cannot run the explain command/db.collection.explain() in executionStats mode or allPlansExecution mode for an aggregation pipeline that contains the $out stage. Instead, you can either:

• queryPlanner モードで explain を実行するか、

• executionStats モード、または allPlansExecution モードで、$out ステージなしでexplain を実行すると、$out ステージに先行するステージの情報が返されます。

explain() Mechanics

The db.collection.explain() method wraps the explain command and is the preferred way to run explain.

db.collection.explain().find() is similar to db.collection.find().explain() with the following key differences:

• The db.collection.explain().find() construct allows for the additional chaining of query modifiers. For list of query modifiers, see db.collection.explain().find().help().

• The db.collection.find().explain() returns the explain() information on the query plan.

db.collection.explain().aggregate() is equivalent to passing the explain option to the db.collection.aggregate() method.

help()

To see the list of operations supported by db.collection.explain(), run:

db.collection.explain().help()

db.collection.explain().find() returns a cursor, which allows for the chaining of query modifiers. To see the list of query modifiers supported by db.collection.explain().find() as well as cursor-related methods, run:

db.collection.explain().find().help()

You can chain multiple modifiers to db.collection.explain().find(). For an example, see Explain find() with Modifiers.

シャーディングされたクラスター

シャーディングされたクラスターに存在しないデータベースに対して db.collection.explain() を実行すると、実行ステージはストリームの終端に達し、操作データベースは作成されません。ストリームの終端の実行統計の詳細については、explain.executionStats.executionStages.isEOF を参照してください。

queryPlanner モード

By default, db.collection.explain() runs in "queryPlanner" verbosity mode.

The following example runs db.collection.explain() in "queryPlanner" verbosity mode to return the query planning information for the specified count() operation:

db.products.explain().count( { quantity: { $gt: 50 } } )

executionStats モード

The following example runs db.collection.explain() in "executionStats" verbosity mode to return the query planning and execution information for the specified find() operation:

db.products.explain("executionStats").find(
   { quantity: { $gt: 50 }, category: "apparel" }
)

allPlansExecution モード

The following example runs db.collection.explain() in "allPlansExecution" verbosity mode. db.collection.explain() returns the queryPlanner and executionStats for all considered plans for the specified findAndModify() operation:

db.products.explain( "allPlansExecution" ).findAndModify( {
   query: { name: "Tom", state: "active", rating: { $gt: 10 } },
   sort: { rating: 1 },
   update: { $inc: { score: 1 } }
} )

修飾語 を使って find() を説明する

db.collection.explain().find() construct allows for the chaining of query modifiers. For example, the following operation provides information on the find() method with sort() and hint() query modifiers.

db.products.explain("executionStats").find(
   { quantity: { $gt: 50 }, category: "apparel" }
).sort( { quantity: -1 } ).hint( { category: 1, quantity: -1 } )

For a list of query modifiers available, run the following in mongosh:

db.collection.explain().find().help()

finish() メソッドで explain() の結果にアクセスする

The db.collection.explain().find() returns the explain() results. If run interactively in mongosh you can use the .finish() method to access the query plan:

db.products.explain().find( { category: "apparel" } ).finish().queryPlanner.winningPlan;