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- PlanCache.listQueryShapes()
PlanCache.listQueryShapes()¶
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Definition¶
-
PlanCache.
listQueryShapes
()¶ Deprecated since version 4.2.
Note
MongoDB 4.2 adds a new aggregation pipeline stage
$planCacheStats
that provides plan cache information for a collection.The
$planCacheStats
aggregation stage is preferred over the following methods and commands, which have been deprecated in 4.2:PlanCache.getPlansByQuery()
method/planCacheListPlans
command, andPlanCache.listQueryShapes()
method/planCacheListQueryShapes
command.
Displays the query shapes for which cached query plans exist.
To help identify slow queries with the same query shape, starting in MongoDB 4.2, each query shape is associated with a queryHash. The
queryHash
is a hexadecimal string that represents a hash of the query shape and is dependent only on the query shape.Note
As with any hash function, two different query shapes may result in the same hash value. However, the occurrence of hash collisions between different query shapes is unlikely.
The query optimizer only caches the plans for those query shapes that can have more than one viable plan.
The method is only available from the
plan cache object
of a specific collection; i.e.Returns: Array of query shape documents. The method wraps the
planCacheListQueryShapes
command.
Required Access¶
On systems running with authorization
, a user must have access that
includes the planCacheRead
action.
Example¶
The following returns the query shapes that have
cached plans for the orders
collection:
The method returns an array of the query shapes currently in the cache.
In the example, the orders
collection had cached query plans
associated with the following shapes:
Note
Not all queries automatically place a query plan in the cache.
db.collection.getPlanCache().listQueryShapes()
returns an empty
array if there are currently no query shapes with cached query plans.