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Query Plan Cache

planCacheClear

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

Definition

planCacheClear

Removes cached query plans for a collection. Specify a plan cache query shape to remove cached query plans for that shape. Omit the plan cache 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.

Query Settings

Starting in MongoDB 8.0, use query settings instead of adding index filters. Index filters are deprecated starting in MongoDB 8.0.

Query settings have more functionality than index filters. Also, index filters aren't persistent and you cannot easily create index filters for all cluster nodes. To add query settings and explore examples, see setQuerySettings.

Compatibility

This command 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 not supported in M0, M2, and M5 clusters. For more information, see Unsupported Commands.

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 plan cache 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 plan cache query shape.
sort
document
Optional. The sort associated with the plan cache 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 Plan Cache Query Shape

If a collection orders has the following plan cache query shape:

{
  "query" : { "qty" : { "$gt" : 10 } },
  "sort" : { "ord_date" : 1 },
  "projection" : { },
  "planCacheShapeHash" : "9AAD95BE"
}

Warning

Starting in MongoDB 8.0, the pre-existing queryHash field is renamed to planCacheShapeHash. If you're using an earlier MongoDB version, you'll see queryHash instead of planCacheShapeHash.

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:

Back

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