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Query Plan Caches

PlanCache.list()

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  • Definition
  • Consideration
  • Required Access
  • Examples

Definition

PlanCache.list(<pipeline>)

Returns an array of plan cache entries for a collection.

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

db.collection.getPlanCache().list(<pipeline>)
Parameter
Type
Description
pipeline
Array

Optional. Aggregation pipeline to filter/process the plan cache query shapes.

You can run this method from a mongod or mongos instance. When run on a sharded cluster, the method returns plan cache entry information from a single member in each shard replica set. This member is identified with the shard and host fields. See also Read Preference.

The method PlanCache.list() wraps the $planCacheStats aggregation pipeline. That is,

db.collection.getPlanCache().list([<stage1>, <stage2>, ...] )

is equivalent to

db.collection.aggregate([ <$planCacheStats stage>, <stage1>, <stage2>, ... ]).toArray();

For details on the output, see $planCacheStats output.

Not all queries automatically place a query plan in the cache. PlanCache.list() returns an empty array if there are currently no plan cache query shapes with cached query plans.

Tip

See also:

Consideration

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.

Restrictions

PlanCache.list() is not allowed in transactions.

Query Hash and Plan Cache Query Shapes

To help identify slow queries with the same plan cache query shape, each plan cache query shape is associated with a query hash. The plan cache query shape hash 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.

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 query optimizer only caches the plan for a plan cache query shape that can have more than one viable plan.

Each entry in the plan cache is associated with a planCacheShapeHash.

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.

Read Preference

PlanCache.list() observes the read preference in selecting the host(s) from which to return the plan cache information.

Applications may target different members of a replica set. As such, each replica set member might receive different read commands and have plan cache information that differs from other members. Nevertheless, running PlanCache.list() on a replica set or a sharded cluster obeys the normal read preference rules. That is, on a replica set, the operation gathers plan cache information from just one member of replica set, and on a sharded cluster, the operation gathers plan cache information from just one member of each shard replica set.

Required Access

On systems running with authorization, the user must have the planCacheRead privilege for the collection.

Examples

Note

  • Not all queries automatically place a query plan in the cache. PlanCache.list() returns an empty array if there are currently no query shapes with cached query plans.

  • For details on the output, see $planCacheStats output.

The examples in this section use the following orders collection:

db.orders.insertMany( [
   { "_id" : 1, "item" : "abc", "price" : NumberDecimal("12"), "quantity" : 2, "type": "apparel" },
   { "_id" : 2, "item" : "jkl", "price" : NumberDecimal("20"), "quantity" : 1, "type": "electronics" },
   { "_id" : 3, "item" : "abc", "price" : NumberDecimal("10"), "quantity" : 5, "type": "apparel" },
   { "_id" : 4, "item" : "abc", "price" : NumberDecimal("8"), "quantity" : 10, "type": "apparel" },
   { "_id" : 5, "item" : "jkl", "price" : NumberDecimal("15"), "quantity" : 15, "type": "electronics" }
] )

Create the following indexes on the collection:

db.orders.createIndex( { item: 1 } );
db.orders.createIndex( { item: 1, quantity: 1 } );
db.orders.createIndex( { item: 1, price: 1 }, { partialFilterExpression: { price: { $gte: NumberDecimal("10")} } } );
db.orders.createIndex( { quantity: 1 } );
db.orders.createIndex( { quantity: 1, type: 1 } );

Note

Index { item: 1, price: 1 } is a partial index and only indexes documents with price field greater than or equal to NumberDecimal("10").

Run some queries against the collection:

db.orders.find( { item: "abc", price: { $gte: NumberDecimal("10") } } )
db.orders.find( { item: "abc", price: { $gte: NumberDecimal("5") } } )
db.orders.find( { quantity: { $gte: 20 } } )
db.orders.find( { quantity: { $gte: 5 }, type: "apparel" } )

Return Information for All Entries in the Query Cache

The following returns the plan cache query shapes that have cached plans for the orders collection:

db.orders.getPlanCache().list()

The method returns an array of the plan cache query shapes currently in the cache. In the example, the orders collection had cached query plans associated with the following shapes:

[
   {
      "createdFromQuery" : {
         "query" : { "quantity" : { "$gte" : 5 }, "type" : "apparel" },
         "sort" : { },
         "projection" : { }
      },
      "planCacheShapeHash" : "4D151C4C",
      "planCacheKey" : "DD67E353",
      "isActive" : false,
      "works" : NumberLong(4),
      "cachedPlan" : {
         "stage" : "FETCH",
         "filter" : { "type" : { "$eq" : "apparel" } },
         "inputStage" : {
            "stage" : "IXSCAN",
            "keyPattern" : { "quantity" : 1 },
            "indexName" : "quantity_1",
            "isMultiKey" : false,
            "multiKeyPaths" : { "quantity" : [ ] },
            "isUnique" : false,
            "isSparse" : false,
            "isPartial" : false,
            "indexVersion" : 2,
            "direction" : "forward",
            "indexBounds" : { "quantity" : [ "[5.0, inf.0]" ] }
         }
      },
      "timeOfCreation" : ISODate("2020-02-06T15:57:18.219Z"),
      "creationExecStats" : [
         {
            "nReturned" : 2,
            "executionTimeMillisEstimate" : 0,
            "totalKeysExamined" : 3,
            "totalDocsExamined" : 3,
            "executionStages" : {
               "stage" : "FETCH",
               "filter" : { "type" : { "$eq" : "apparel" } },
               "nReturned" : 2,
               "executionTimeMillisEstimate" : 0,
               "works" : 4,
               ...
            }
         },
         {
            "nReturned" : 2,
            "executionTimeMillisEstimate" : 0,
            "totalKeysExamined" : 3,
            "totalDocsExamined" : 2,
            "executionStages" : {
               "stage" : "FETCH",
               "nReturned" : 2,
               "executionTimeMillisEstimate" : 0,
               "works" : 4,
               ...
            }
         }
      ],
      "candidatePlanScores" : [
         1.5002,
         1.5002
      ],
      "indexFilterSet" : false,
      "estimatedSizeBytes" : NumberLong(3160),   // Available starting in MongoDB 5.0
      "host" : "mongodb1.example.net:27018",
      "shard" : "shardA"                         // Available if run on sharded cluster
   },
   {
      "createdFromQuery" : {
         "query" : { "quantity" : { "$gte" : 20 } },
         "sort" : { },
         "projection" : { }
      },
      "planCacheShapeHash" : "23B19B75",
      "planCacheKey" : "6F23F858",
      "isActive" : false,
      "works" : NumberLong(1),
      ...
   },
   {
      "createdFromQuery" : {
         "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("5") } },
         "sort" : { },
         "projection" : { }
      },
      "planCacheShapeHash" : "117A6B10",
      "planCacheKey" : "A1824628",
      "isActive" : false,
      "works" : NumberLong(4),
      ...
   },
   {
      "createdFromQuery" : {
         "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("10") } },
         "sort" : { },
         "projection" : { }
      },
      "planCacheShapeHash" : "117A6B10",
      "planCacheKey" : "2E6E536B",
      "isActive" : false,
      "works" : NumberLong(3),
      ...
   }
]

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.

For details on the output, see $planCacheStats output.

List Plan Cache Query Shapes

To obtain a list of all of the query shapes for which there is a cached plan, you can use the PlanCache.list(). For example, the following operation passes in a pipeline with a $project stage to only output the createdFromQuery field and the planCacheShapeHash field.

db.orders.getPlanCache().list( [ { $project: {createdFromQuery: 1, planCacheShapeHash: 1 } } ] )

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 operation returns the following plan cache query shapes:

[
   { "createdFromQuery" : { "query" : { "quantity" : { "$gte" : 5 }, "type" : "apparel" }, "sort" : { }, "projection" : { } }, "planCacheShapeHash" : "4D151C4C" },
   { "createdFromQuery" : { "query" : { "quantity" : { "$gte" : 20 } }, "sort" : { }, "projection" : { } }, "planCacheShapeHash" : "23B19B75" },
   { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("5") } }, "sort" : { }, "projection" : { } }, "planCacheShapeHash" : "117A6B10" },
   { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("10") } }, "sort" : { }, "projection" : { } }, "planCacheShapeHash" : "117A6B10" }
]

For details on the output, see $planCacheStats output.

Find Cache Entry Details for a Plan Cache Query Shape

To return plan cache information for a particular query shape, pass in a pipeline with a $match on the planCacheKey field.

db.orders.getPlanCache().list([ { $match: { planCacheKey: "DD67E353"} } ] )

The operation returns the following:

[
   {
      "createdFromQuery" : {
         "query" : {
            "quantity" : {
               "$gte" : 5
            },
            "type" : "apparel"
         },
         "sort" : {
         },
         "projection" : {
         }
      },
      "planCacheShapeHash" : "4D151C4C",
      "planCacheKey" : "DD67E353",
      "isActive" : false,
      "works" : NumberLong(4),
      "cachedPlan" : {
         "stage" : "FETCH",
         "filter" : {
            "type" : {
               "$eq" : "apparel"
            }
         },
         "inputStage" : {
            "stage" : "IXSCAN",
            "keyPattern" : {
               "quantity" : 1
            },
            "indexName" : "quantity_1",
            "isMultiKey" : false,
            "multiKeyPaths" : {
               "quantity" : [ ]
            },
            "isUnique" : false,
            "isSparse" : false,
            "isPartial" : false,
            "indexVersion" : 2,
            "direction" : "forward",
            "indexBounds" : {
               "quantity" : [
                  "[5.0, inf.0]"
               ]
            }
         }
      },
      "timeOfCreation" : ISODate("2020-02-11T17:14:33.873Z"),
      "creationExecStats" : [
         {
            "nReturned" : 2,
            "executionTimeMillisEstimate" : 0,
            "totalKeysExamined" : 3,
            "totalDocsExamined" : 3,
            "executionStages" : {
               "stage" : "FETCH",
               "filter" : {
                  "type" : {
                     "$eq" : "apparel"
                  }
               },
               "nReturned" : 2,
               "executionTimeMillisEstimate" : 0,
               "works" : 4,
               "advanced" : 2,
               "needTime" : 1,
               "needYield" : 0,
               "saveState" : 0,
               "restoreState" : 0,
               "isEOF" : 1,
               "docsExamined" : 3,
               "alreadyHasObj" : 0,
               "inputStage" : {
                  "stage" : "IXSCAN",
                  "nReturned" : 3,
                  "executionTimeMillisEstimate" : 0,
                  "works" : 4,
                  "advanced" : 3,
                  "needTime" : 0,
                  "needYield" : 0,
                  "saveState" : 0,
                  "restoreState" : 0,
                  "isEOF" : 1,
                  "keyPattern" : {
                     "quantity" : 1
                  },
                  "indexName" : "quantity_1",
                  "isMultiKey" : false,
                  "multiKeyPaths" : {
                     "quantity" : [ ]
                  },
                  "isUnique" : false,
                  "isSparse" : false,
                  "isPartial" : false,
                  "indexVersion" : 2,
                  "direction" : "forward",
                  "indexBounds" : {
                     "quantity" : [
                        "[5.0, inf.0]"
                     ]
                  },
                  "keysExamined" : 3,
                  "seeks" : 1,
                  "dupsTested" : 0,
                  "dupsDropped" : 0
               }
            }
         },
         {
            "nReturned" : 2,
            "executionTimeMillisEstimate" : 0,
            "totalKeysExamined" : 3,
            "totalDocsExamined" : 2,
            "executionStages" : {
               "stage" : "FETCH",
               "nReturned" : 2,
               "executionTimeMillisEstimate" : 0,
               "works" : 4,
               "advanced" : 2,
               "needTime" : 1,
               "needYield" : 0,
               "saveState" : 0,
               "restoreState" : 0,
               "isEOF" : 1,
               "docsExamined" : 2,
               "alreadyHasObj" : 0,
               "inputStage" : {
                  "stage" : "IXSCAN",
                  "nReturned" : 2,
                  "executionTimeMillisEstimate" : 0,
                  "works" : 4,
                  "advanced" : 2,
                  "needTime" : 1,
                  "needYield" : 0,
                  "saveState" : 0,
                  "restoreState" : 0,
                  "isEOF" : 1,
                  "keyPattern" : {
                     "quantity" : 1,
                     "type" : 1
                  },
                  "indexName" : "quantity_1_type_1",
                  "isMultiKey" : false,
                  "multiKeyPaths" : {
                     "quantity" : [ ],
                     "type" : [ ]
                  },
                  "isUnique" : false,
                  "isSparse" : false,
                  "isPartial" : false,
                  "indexVersion" : 2,
                  "direction" : "forward",
                  "indexBounds" : {
                     "quantity" : [
                        "[5.0, inf.0]"
                     ],
                     "type" : [
                        "[\"apparel\", \"apparel\"]"
                     ]
                  },
                  "keysExamined" : 3,
                  "seeks" : 2,
                  "dupsTested" : 0,
                  "dupsDropped" : 0
               }
            }
         }
      ],
      "candidatePlanScores" : [
         1.5002,
         1.5002
      ],
      "indexFilterSet" : false,
      "estimatedSizeBytes" : NumberLong(3160),   // Available starting in MongoDB 5.0
      "host" : "mongodb1.example.net:27018",
      "shard" : "shardA"                         // Available if run on sharded cluster
   }
]

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.

For details on the output, see $planCacheStats output.

Back

PlanCache.help