PlanCache.getPlansByQuery()

PlanCache.getPlansByQuery()

Definition

PlanCache.getPlansByQuery(, , )

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 overthe following methods and commands, which have been deprecated in 4.2:

PlanCache.getPlansByQuery()method/planCacheListPlans command, and
PlanCache.listQueryShapes()method/planCacheListQueryShapes command.

Displays the cached query plans for the specified queryshape.

To help identify slow queries with the same query shape,starting in MongoDB 4.2, each query shape is associated witha queryHash. The queryHash is ahexadecimal string that represents a hash of the query shape andis dependent only on the query shape.

Note

As with any hash function, two different query shapes may resultin the same hash value. However, the occurrence of hashcollisions between different query shapes is unlikely.

The query optimizer only caches the plans for those query shapes thatcan have more than one viable plan.

The method is only available from the plan cache object of a specific collection; i.e.

db.collection.getPlanCache().getPlansByQuery( <query>, <projection>, <sort> )

The PlanCache.getPlansByQuery() method accepts thefollowing parameters:

ParameterTypeDescriptionquerydocumentThe query predicate of the query shape. Only the structureof the predicate, including the field names, are significant to theshape; the values in the query predicate are insignificant.projectiondocumentOptional. The projection associated with the query shape. Required ifspecifying the sort parameter.sortdocumentOptional. The sort associated with the query shape.

Returns:Array of cached query plans for a query shape.

To see the query shapes for which cached query plans exist, seeList Query Shapes.

The PlanCache.getPlansByQuery() method returns the sameoutput as the planCacheListPlans database command.

Required Access

On systems running with authorization, a user must have access thatincludes the planCacheRead action.

Example

If a collection orders has the following query shape:

{
  "query" : { "qty" : { "$gt" : 10 } },
  "sort" : { "ord_date" : 1 },
  "projection" : { },
  "queryHash" : "9AAD95BE"  // Available starting in MongoDB 4.2
}

The following operation displays the query plan cached for the shape:

db.orders.getPlanCache().getPlansByQuery(
   { "qty" : { "$gt" : 10 } },
   { },
   { "ord_date" : 1 }
)