cursor.explain()
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Definition
cursor.explain(verbosity)
Important
mongosh Method
This page documents a
mongosh
method. This is not the documentation for a language-specific driver, such as Node.js.For MongoDB API drivers, refer to the language-specific MongoDB driver documentation.
Provides information on the query plan for the
db.collection.find()
method.The
explain()
method has the following form:db.collection.find().explain() The
explain()
method has the following parameter:ParameterNecessityTypeDescriptionverbose
OptionalStringDetermines the amount of information to include in the explain output. The possible verbosity modes are:
allPlansExecution
executionStats
queryPlanner
(Default)
For backwards compatibility with earlier versions of
explain()
, MongoDB interpretstrue
asallPlansExecution
andfalse
asqueryPlanner
.For more information on the modes, see Verbosity Modes.
The
explain()
method returns a document with the query plan and, optionally, the execution statistics.
Compatibility
This method is available in deployments hosted in the following environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
Note
This command is supported in all MongoDB Atlas clusters. For information on Atlas support for all commands, see Unsupported Commands.
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Behavior
Note
Using explain
ignores all existing plan cache entries and prevents
the MongoDB query planner from creating a new plan cache entry.
Verbosity Modes
The behavior of cursor.explain()
and the amount of
information returned depend on the verbosity
mode.
queryPlanner
Mode
By default, cursor.explain()
runs in queryPlanner
verbosity mode.
MongoDB runs the query optimizer to choose
the winning plan for the operation under evaluation. cursor.explain()
returns
the queryPlanner
information for the evaluated
method.
executionStats
Mode
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.
cursor.explain()
returns the queryPlanner
and
executionStats
information for the evaluated
method. However, executionStats
does not
provide query execution information for the rejected plans.
allPlansExecution
Mode
MongoDB runs the query optimizer to choose the winning plan and executes the
winning plan to completion. 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.
cursor.explain()
returns the queryPlanner
and
executionStats
information for the evaluated
method. The executionStats
includes the
completed query execution information for the winning plan.
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.
db.collection.explain().find()
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 a cursor, which requires a call to.next()
, or its alias.finish()
, to return theexplain()
results. If run interactively inmongosh
,mongosh
automatically calls.finish()
to return the results. For scripts, however, you must explicitly call.next()
, or.finish()
, to return the results. For list of cursor-related methods, see db.collection.explain().find().help().
See db.collection.explain()
for more information.
Output
cursor.explain()
operations can return information regarding:
explainVersion
, the output format version (for example,"1"
).command
, which details the command being explained.queryShapeHash
, starting in MongoDB 8.0, which is a hexadecimal string with the hash of a query shape. For details, see Query Shapes, Query Shape Hash, andexplain.queryShapeHash
.queryPlanner
, which details the plan selected by the query optimizer and lists the rejected plans.executionStats
, which details the execution of the winning plan and the rejected plans.serverInfo
, which provides information on the MongoDB instance.serverParameters
, which details internal parameters.
The verbosity mode (i.e. queryPlanner
, executionStats
,
allPlansExecution
) determines whether the results include
executionStats
and whether executionStats
includes data
captured during plan selection.
Explain output is limited by the maximum Nested Depth for BSON Documents, which is 100 levels of nesting. Explain output that exceeds the limit is truncated.
For details on the output, see Explain Results.
Example
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:
db.products.find( { quantity: { $gt: 50 }, category: "apparel" } ).explain("executionStats")