db.collection.explain() (mongosh method方法)

Verbosity Modes详细模式

The behavior of db.collection.explain() and the amount of information returned depend on the verbosity mode.db.collection.explain()的行为和返回的信息量取决于verbosity模式。

Explain and Write Operations解释和编写操作

For write operations, db.collection.explain() returns information about the write operation that would be performed but does not actually modify the database.对于写操作，db.collection.explain()返回有关将要执行但实际上不会修改数据库的写操作的信息。

Restrictions限制

You cannot run the explain command/db.collection.explain() in executionStats mode or allPlansExecution mode for an aggregation pipeline that contains the $out stage. Instead, you can either:对于包含$out阶段的聚合管道，您无法在executionStats模式或allPlansExecution模式下运行explain命令/db.collection.explain()。相反，您可以：

• run the explain in queryPlanner mode or在queryPlanner模式下运行解释，或
• run the explain in executionStats mode or allPlansExecution mode but without the $out stage to return information for the stages that precede the $out stage.在executionStats模式或allPlansExecution模式下运行解释，但不运行$out阶段，以返回$out阶段之前阶段的信息。

explain() Mechanics机制

The db.collection.explain() method wraps the explain command and is the preferred way to run explain.db.collection.explain()方法封装了explain命令，是运行explain的首选方式。

db.collection.explain().find() is similar to db.collection.find().explain() with the following key differences:与db.collection.find().explain()类似，但有以下关键区别：

• 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().db.collection.explain().find()构造允许额外的查询修饰符链接。有关查询修饰符的列表，请参阅db.collection.explain().find().help()。
• The db.collection.find().explain() returns the explain() information on the query plan.返回查询计划的explain()信息。

db.collection.explain().aggregate() is equivalent to passing the explain option to the db.collection.aggregate() method.相当于将解释选项传递给db.collection.aggregate()方法。

help()

To see the list of operations supported by db.collection.explain(), run:要查看db.collection.explain()支持的操作列表，请运行：

db.collection.explain().help()

db.collection.explain().find() returns a cursor, which allows for the chaining of query modifiers. 返回一个游标，它允许链接查询修饰符。To see the list of query modifiers supported by db.collection.explain().find() as well as cursor-related methods, run:要查看db.collection.explain().find()支持的查询修饰符列表以及与游标相关的方法，请运行：

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

You can chain multiple modifiers to db.collection.explain().find(). For an example, see Explain find() with Modifiers.您可以将多个修饰符链接到db.collection.explain().find()。例如，请参阅使用修饰符解释find()。

queryPlanner Mode模式

By default, db.collection.explain() runs in "queryPlanner" verbosity mode.默认情况下，db.collection.explain()在"queryPlanner"详细模式下运行。

The following example runs db.collection.explain() in "queryPlanner" verbosity mode to return the query planning information for the specified count() operation:以下示例在"queryPlanner"详细程度模式下运行db.collection.explain()，以返回指定count()操作的查询计划信息：

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

executionStats Mode模式

The following example runs db.collection.explain() in "executionStats" verbosity mode to return the query planning and execution information for the specified find() operation:以下示例在"executionStats"详细程度模式下运行db.collection.explain()，以返回指定find()操作的查询计划和执行信息：

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

allPlansExecution Mode模式

The following example runs db.collection.explain() in "allPlansExecution" verbosity mode. 以下示例在"allPlansExecution"详细模式下运行db.collection.explain()。db.collection.explain() returns the queryPlanner and executionStats for all considered plans for the specified findAndModify() operation:db.collection.explain()为指定的findAndModify()操作返回所有考虑的计划的queryPlanner和executionStats：

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

Explain find() with Modifiers用修饰符解释find()

db.collection.explain().find() construct allows for the chaining of query modifiers. 构造允许链接查询修饰符。For example, the following operation provides information on the find() method with sort() and hint() query modifiers.例如，以下操作提供了有关带有sort()和hint()查询修饰符的find()方法的信息。

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:有关可用查询修饰符的列表，请在mongosh中运行以下命令：

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

Access the explain() Results with finish() Method使用finish()方法访问explain()结果

The db.collection.explain().find() returns the explain() results. db.collection.explain().find()返回explain()结果。If run interactively in mongosh you can use the .finish() method to access the query plan:如果在mongosh中以交互方式运行，则可以使用.finish()方法访问查询计划：

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