cursor.explain()

On this page本页内容

Definition定义

cursor.explain(verbosity)
Important重要
mongosh Method

This is a mongosh method. This is not the documentation for Node.js or other programming language specific driver methods.

In most cases, mongosh methods work the same way as the legacy mongo shell methods. However, some legacy methods are unavailable in mongosh.

For the legacy mongo shell documentation, refer to the documentation for the corresponding MongoDB Server release:

For MongoDB API drivers, refer to the language specific MongoDB driver documentation.

Provides information on the query plan for the db.collection.find() method.提供有关db.collection.find()方法的查询计划的信息。

The explain() method has the following form:explain()方法具有以下形式：

db.collection.find().explain()

The explain() method has the following parameter:explain()方法具有以下参数：

Parameter参数Type类型Description描述
verbosestring

Optional. 可选。Specifies the verbosity mode for the explain output. 指定解释输出的详细模式。The mode affects the behavior of explain() and determines the amount of information to return. 模式会影响explain()的行为，并确定要返回的信息量。The possible modes are: "queryPlanner", "executionStats", and "allPlansExecution".可能的模式有："queryPlanner"、"executionStats"和"allPlansExecution"。

Default mode is "queryPlanner".默认模式为"queryPlanner"。

For backwards compatibility with earlier versions of cursor.explain(), MongoDB interprets true as "allPlansExecution" and false as "queryPlanner".为了向后兼容早期版本的cursor.explain()，MongoDB将true解释为"allPlansExecution"，将false解释为"queryPlanner"。

For more information on the modes, see Verbosity Modes.有关模式的详细信息，请参阅详细模式。

The explain() method returns a document with the query plan and, optionally, the execution statistics.explain()方法返回一个文档，其中包含查询计划和可选的执行统计信息。

Behavior行为

Verbosity Modes详细信息模式

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

queryPlanner Mode模式

By default, cursor.explain() runs in queryPlanner verbosity mode.默认情况下，cursor.explain()以queryPlanner详细模式运行。

MongoDB runs the query optimizer to choose the winning plan for the operation under evaluation. MongoDB运行查询优化器，为正在评估的操作选择获胜的计划。cursor.explain() returns the queryPlanner information for the evaluated method.返回计算方法的queryPlanner信息。

executionStats Mode模式

MongoDB runs the query optimizer to choose the winning plan, executes the winning plan to completion, and returns statistics describing the execution of the winning plan.MongoDB运行查询优化器来选择获胜计划，执行获胜计划直到完成，并返回描述获胜计划执行情况的统计信息。

cursor.explain() returns the queryPlanner and executionStats information for the evaluated method. 返回计算方法的queryPlanner和executionStats信息。However, executionStats does not provide query execution information for the rejected plans.但是，executionStats不为被拒绝的计划提供查询执行信息。

allPlansExecution Mode模式

MongoDB runs the query optimizer to choose the winning plan and executes the winning plan to completion. MongoDB运行查询优化器来选择获胜计划，并执行获胜计划直至完成。In "allPlansExecution" mode, MongoDB returns statistics describing the execution of the winning plan as well as statistics for the other candidate plans captured during plan selection.在"allPlansExecution"模式下，MongoDB返回描述获胜计划执行情况的统计信息，以及计划选择期间捕获的其他候选计划的统计信息。

cursor.explain() returns the queryPlanner and executionStats information for the evaluated method. cursor.explain()返回计算方法的queryPlanner和executionStats信息。The executionStats includes the completed query execution information for the winning plan.executionStats包括获胜计划的已完成查询执行信息。

If the query optimizer considered more than one plan, executionStats information also includes the partial execution information captured during the plan selection phase for both the winning and rejected candidate plans.如果查询优化器考虑了多个计划，那么executionStats信息还包括在计划选择阶段为获胜和被拒绝的候选计划捕获的部分执行信息。

db.collection.explain().find()

db.collection.explain().find() is similar to db.collection.find().explain() with the following key differences:与db.collection.find().explain()类似，但有以下主要区别：

See db.collection.explain() for more information.有关详细信息，请参阅db.collection.explain()。

Output输出

cursor.explain() operations can return information regarding:操作可以返回有关以下内容的信息：

  • explainVersion, the output format version (for example, "1");，输出格式版本（例如，"1"）；
  • command, which details the command being explained;，其中详细说明了所解释的命令；
  • queryPlanner, which details the plan selected by the query optimizer and lists the rejected plans;，详细说明查询优化器选择的计划并列出被拒绝的计划；
  • executionStats, which details the execution of the winning plan and the rejected plans;详细说明中标计划和被拒计划的执行情况；
  • serverInfo, which provides information on the MongoDB instance; and，提供MongoDB实例信息；以及
  • serverParameters, which details internal parameters.，其中详细说明了内部参数。

The verbosity mode (i.e. queryPlanner, executionStats, allPlansExecution) determines whether the results include executionStats and whether executionStats includes data captured during plan selection.详细模式（即queryPlanner、executionStats、allPlansExecution）确定结果是否包含executionStats，以及executionStats是否包含在计划选择期间捕获的数据。

Explain output is limited by the maximum Nested Depth for BSON Documents, which is 100 levels of nesting. 解释输出受BSON文档的最大嵌套深度限制，即100级嵌套。Explain output that exceeds the limit is truncated.解释超出限制的输出被截断。

For details on the output, see Explain Results.有关输出的详细信息，请参阅解释结果。

Example示例

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

db.products.find(
   { quantity: { $gt: 50 }, category: "apparel" }
).explain("executionStats")
←  cursor.count()cursor.forEach() →