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PlanCache.listQueryShapes()

Definition

PlanCache.listQueryShapes()

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 PlanCache.getPlansByQuery() method/planCacheListPlans command and PlanCache.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.

db.collection.getPlanCache().listQueryShapes()
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:

db.orders.getPlanCache().listQueryShapes()

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:

[
  {
    "query" : { "qty" : { "$gt" : 10 } },
    "sort" : { "ord_date" : 1 },
    "projection" : { },
    "queryHash" : "9AAD95BE" // Available starting in MongoDB 4.2
  },
  {
    "query" : { "$or" :
       [
         { "qty" : { "$gt" : 15 }, "item" : "xyz123" },
         { "status" : "A" }
       ]
    },
    "sort" : { },
    "projection" : { },
    "queryHash" : "0A087AD0"  // Available starting in MongoDB 4.2
  },
  {
    "query" : { "$or" : [ { "qty" : { "$gt" : 15 } }, { "status" : "A" } ] },
    "sort" : { },
    "projection" : { },
    "queryHash" : "DA43B020"
  }
]

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.