$planCacheStats

Pipeline管道

$planCacheStats must be the first stage in an aggregation pipeline.必须是聚合管道中的第一个阶段。

Restrictions限制

• $planCacheStats is not allowed in:不允许出现在：
  • transactions事务
  • $facet aggregation stage聚合阶段
• $planCacheStats requires read concern level "local".需要读取关注级别"local"。

Access Control访问控制

On systems running with authorization, the user must have the planCacheRead privilege for the collection.在使用authorization运行的系统上，用户必须具有集合的planCacheRead权限。

Redaction

When using Queryable Encryption, the $planCacheStats stage omits operations against encrypted collections, even though the operations are cached as normal.使用可查询加密时，$planCacheStats阶段会省略针对加密集合的操作，即使这些操作是正常缓存的。

Read Preference读取首选项

$planCacheStats observes the read preference in selecting the host(s) from which to return the plan cache information.在选择从其返回计划高速缓存信息的主机时观察读取偏好。

Applications may target different members of a replica set. 应用程序可以针对副本集的不同成员。As such, each replica set member might receive different read commands and have plan cache information that differs from other members. 因此，每个副本集成员可能接收不同的读取命令，并且具有与其他成员不同的计划缓存信息。Nevertheless, running $planCacheStats on a replica set or a sharded cluster obeys the normal read preference rules. 然而，在副本集或分片集群上运行$planCacheStats遵循正常的读取偏好规则。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.也就是说，在副本集中，该操作仅从副本集中的一个成员集合计划缓存信息，而在分片集群中，该操作从每个分片副本集中的仅一个成员中集合计划高速缓存信息。

Return Information for All Entries in the Query Cache返回查询缓存中所有条目的信息

The following aggregation pipeline uses $planCacheStats to return information on the plan cache entries for the collection:以下聚合管道使用$planCacheStats返回集合的计划缓存项的信息：

db.orders.aggregate( [
   { $planCacheStats: { } }
] )

Output:输出：

[
  {                                             // Plan Cache Entry 1
    version: '2',
    queryHash: '478AD696',
    planCacheKey: '21AE23AD',
    isActive: true,
    works: Long("7"),
    timeOfCreation: ISODate("2023-05-22T20:33:49.031Z"),
    cachedPlan: {
      ...
    },
    indexFilterSet: false,
    isPinned: false,
    estimatedSizeBytes: Long("8194"),
    host: 'mongodb1.example.net:27018'
  },
  {                                             // Plan Cache Entry 2
       version: '2',
       queryHash: '3D8AFDC6',
       planCacheKey: '1C2C4360',
       isActive: true,
       works: Long("6"),
       timeOfCreation: ISODate("2023-05-22T20:33:50.584Z"),
       cachedPlan: {
         ...
       },
       indexFilterSet: false,
       isPinned: false,
       estimatedSizeBytes: Long("11547"),
       host: 'mongodb1.example.net:27018'
     },
     {                                          // Plan Cache Entry 3
       version: '2',
       queryHash: '27285F9B',
       planCacheKey: '20BB9404',
       isActive: true,
       works: Long("1"),
       timeOfCreation: ISODate("2023-05-22T20:33:49.051Z"),
       cachedPlan: {
         ...
       },
       indexFilterSet: false,
       isPinned: false,
       estimatedSizeBytes: Long("7406"),
       host: 'mongodb1.example.net:27018'
     },
     {                                          // Plan Cache Entry 4
       version: '2',
       queryHash: '478AD696',
       planCacheKey: 'B1435201',
       isActive: true,
       works: Long("5"),
       timeOfCreation: ISODate("2023-05-22T20:33:49.009Z"),
       cachedPlan: {
         ...
       },
       indexFilterSet: false,
       isPinned: false,
       estimatedSizeBytes: Long("7415"),
       host: 'mongodb1.example.net:27018'
     }
   ],

See also planCacheKey.另请参见planCacheKey。

Find Cache Entry Details for a Query Hash查找查询哈希的缓存项详细信息

To return plan cache information for a particular query hash, the $planCacheStats stage can be followed by a $match on the planCacheKey field.要返回特定查询哈希的计划缓存信息，可以在$planCacheStats阶段后面的planCacheKey字段中添加$match。

The following aggregation pipeline uses $planCacheStats followed by a $match stage to return specific information for a particular query hash:以下聚合管道使用$planCacheStats和$match阶段来返回特定查询哈希的特定信息：

db.orders.aggregate( [
   { $planCacheStats: { } },
   { $match: { planCacheKey: "B1435201"} }
] )

Output:输出：

[
  {
    version: '2',
    queryHash: '478AD696',
    planCacheKey: 'B1435201',
    isActive: true,
    works: Long("5"),
    timeOfCreation: ISODate("2023-05-22T20:33:49.009Z"),
    cachedPlan: {
      slots: '$$RESULT=s11 env: { s3 = 1684787629009 (NOW), s6 = Nothing, s5 = Nothing, s1 = TimeZoneDatabase(Asia/Kuwait...Etc/UCT) (timeZoneDB), s10 = {"item" : 1, "price" : 1}, s2 = Nothing (SEARCH_META) }',
      stages: '[2] nlj inner [] [s4, s7, s8, s9, s10] \n' +
        '    left \n' +
        '        [1] cfilter {(exists(s5) && exists(s6))} \n' +
        '        [1] ixseek s5 s6 s9 s4 s7 s8 [] @"358822b7-c129-47b7-ad7f-40017a51b03c" @"item_1_price_1" true \n' +
        '    right \n' +
        '        [2] limit 1 \n' +
        '        [2] seek s4 s11 s12 s7 s8 s9 s10 none none [] @"358822b7-c129-47b7-ad7f-40017a51b03c" true false \n'
    },
    indexFilterSet: false,
    isPinned: false,
    estimatedSizeBytes: Long("7415"),
    host: 'mongodb1.example.net:27018'
  }
]

See also planCacheKey and queryHash.另请参阅planCacheKey和queryHash。