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Query Plan Cache Commands

planCacheClear

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  • Definition
  • Syntax
  • Command Fields
  • Required Access
  • Examples

Definition

planCacheClear

Removes cached query plans for a collection. Specify a query shape to remove cached query plans for that shape. Omit the query shape to clear all cached query plans.

Tip

In mongosh, this command can also be run through the PlanCache.clear() and PlanCache.clearPlansByQuery() helper methods.

Helper methods are convenient for mongosh users, but they may not return the same level of information as database commands. In cases where the convenience is not needed or the additional return fields are required, use the database command.

Syntax

The command has the following syntax:

db.runCommand(
   {
      planCacheClear: <collection>,
      query: <query>,
      sort: <sort>,
      projection: <projection>,
      comment: <any>
   }
)

Command Fields

The command takes the following optional fields:

Field
Type
Description
query
document
Optional. The query predicate of the query shape. Only the structure of the predicate, including the field names, are significant to the shape; the values in the query predicate are insignificant.
projection
document
Optional. The projection associated with the query shape.
sort
document
Optional. The sort associated with the query shape.
comment
any

Optional. A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations:

A comment can be any valid BSON type (string, integer, object, array, etc).

To see the query shapes for which cached query plans exist, see Examples.

Required Access

On systems running with authorization, a user must have access that includes the planCacheWrite action.

Examples

Clear Cached Plans for a Query Shape

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 clears the query plan cached for the shape:

db.runCommand(
   {
      planCacheClear: "orders",
      query: { "qty" : { "$gt" : 10 } },
      sort: { "ord_date" : 1 }
   }
)

Clear All Cached Plans for a Collection

The following example clears all the cached query plans for the orders collection:

db.runCommand(
   {
      planCacheClear: "orders"
   }
)

Tip

See also:

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Query Plan Cache Commands