PlanCache.list()
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Definition
PlanCache.list(<pipeline>)Returns an array of plan cache entries for a collection.
The method is only available from the
plan cache objectof a specific collection; i.e.db.collection.getPlanCache().list(<pipeline>) ParameterTypeDescriptionArrayOptional. Aggregation pipeline to filter/process the query shapes.
You can run this method from a
mongodormongosinstance. 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$planCacheStatsaggregation pipeline. That is,db.collection.getPlanCache().list([<stage1>, <stage2>, ...] ) is equivalent to
db.collection.aggregate([ <$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 query shapes with cached query plans.
Consideration
Restrictions
PlanCache.list() is not allowed in transactions.
Query Hash and Query Shapes
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.
Each entry in the plan cache is associated with a queryHash.
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: { $gte: 5 }, type: "apparel" } )
Return Information for All Entries in the Query Cache
The following returns the query shapes that have
cached plans for the orders collection:
db.orders.getPlanCache().list()
The method returns an array of the query shapes currently in the cache.
In the example, the orders collection had cached query plans
associated with the following shapes:
[ { "createdFromQuery" : { "query" : { "quantity" : { "$gte" : 5 }, "type" : "apparel" }, "sort" : { }, "projection" : { } }, "queryHash" : "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" : { "$gte" : 20 } }, "sort" : { }, "projection" : { } }, "queryHash" : "23B19B75", "planCacheKey" : "6F23F858", "isActive" : false, "works" : NumberLong(1), ... }, { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("5") } }, "sort" : { }, "projection" : { } }, "queryHash" : "117A6B10", "planCacheKey" : "A1824628", "isActive" : false, "works" : NumberLong(4), ... }, { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("10") } }, "sort" : { }, "projection" : { } }, "queryHash" : "117A6B10", "planCacheKey" : "2E6E536B", "isActive" : false, "works" : NumberLong(3), ... } ]
For details on the output, see $planCacheStats output.
List 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
queryHash field.
db.orders.getPlanCache().list( [ { $project: {createdFromQuery: 1, queryHash: 1 } } ] )
The operation returns the following query shapes:
[ { "createdFromQuery" : { "query" : { "quantity" : { "$gte" : 5 }, "type" : "apparel" }, "sort" : { }, "projection" : { } }, "queryHash" : "4D151C4C" }, { "createdFromQuery" : { "query" : { "quantity" : { "$gte" : 20 } }, "sort" : { }, "projection" : { } }, "queryHash" : "23B19B75" }, { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("5") } }, "sort" : { }, "projection" : { } }, "queryHash" : "117A6B10" }, { "createdFromQuery" : { "query" : { "item" : "abc", "price" : { "$gte" : NumberDecimal("10") } }, "sort" : { }, "projection" : { } }, "queryHash" : "117A6B10" } ]
For details on the output, see $planCacheStats output.
Find Cache Entry Details for a 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" : { } }, "queryHash" : "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 } ]
For details on the output, see $planCacheStats output.