$collStats (aggregation)

Redaction修改

When using Queryable Encryption, $collStats output redacts certain information for encrypted collections:使用可查询加密时，$collStats输出会对加密集合的某些信息进行编辑：

• The output omits 输出省略"queryExecStats"
• The output omits 输出省略"latencyStats"
• The output redacts "WiredTiger", if present, to include only the url field.输出对"WiredTiger"（如果存在）进行编辑，以仅包括url字段。

Transactions事务

$collStats is not allowed in transactions.事务记录中不允许有$collStats。

latencyStats Document文档

The latencyStats embedded document only exists in the output if you specify the latencyStats option.如果指定latencyStats选项，则latencyStatis嵌入文档仅存在于输出中。

Each of these fields contains an embedded document bearing the following fields:这些字段中的每一个都包含一个嵌入文档，其中包含以下字段：

histogram: [
  { micros: NumberLong(1), count: NumberLong(10) },
  { micros: NumberLong(2), count: NumberLong(1) },
  { micros: NumberLong(4096), count: NumberLong(1) },
  { micros: NumberLong(16384), count: NumberLong(1000) },
  { micros: NumberLong(49152), count: NumberLong(100) }
]

For example, if you run $collStats with the latencyStats: {} option on a matrices collection:例如，如果在matrices集合上使用latencyStats: {}选项运行$collStats：

db.matrices.aggregate( [ { $collStats: { latencyStats: { histograms: true } } } ] )

This query returns a result similar to the following:此查询返回类似于以下内容的结果：

{ "ns" : "test.matrices",
  "host" : mongo.example.net:27017",
  "localTime" : ISODate("2017-10-06T19:43:56.599Z"),
  "latencyStats" :
    { "reads" :
        { "histogram" : [
            { "micros" : NumberLong(16),
              "count" : NumberLong(3) },
            { "micros" : NumberLong(32),
              "count" : NumberLong(1) },
            { "micros" : NumberLong(128),
              "count" : NumberLong(1) } ],
          "latency" : NumberLong(264),
          "ops" : NumberLong(5) },
      "writes" :
        { "histogram" : [
            { "micros" : NumberLong(32),
              "count" : NumberLong(1) },
            { "micros" : NumberLong(64),
              "count" : NumberLong(3) },
            { "micros" : NumberLong(24576),
              "count" : NumberLong(1) } ],
          "latency" : NumberLong(27659),
          "ops" : NumberLong(5) },
      "commands" :
        { "histogram" : [
            {
               "micros" : NumberLong(196608),
               "count" : NumberLong(1)
            }
          ],
          "latency" : NumberLong(0),
          "ops" : NumberLong(0) },
      "transactions" : {
         "histogram" : [ ],
         "latency" : NumberLong(0),
         "ops" : NumberLong(0)
      }
    }
}

storageStats Document文档

The storageStats embedded document only exists in the output if you specify the storageStats option.只有在指定storageStats选项的情况下，storageStat嵌入文档才会出现在输出中。

The contents of this document are dependent on the storage engine in use. 本文档的内容取决于所使用的存储引擎。See Output for a reference on this document.有关本文档的参考信息，请参阅输出。

For example, if you run $collStats with the storageStats: {} option on a matrices collection using the WiredTiger Storage Engine:例如，如果使用WiredTiger存储引擎在矩阵集合上运行带有storageStats:{}选项的$collStats：

db.matrices.aggregate( [ { $collStats: { storageStats: { } } } ] )

This query returns a result similar to the following:此查询返回类似于以下内容的结果：

{
  "ns" : "test.matrices",
  "host" : mongo.example.net:27017",
  "localTime" : ISODate("2020-03-06T01:44:57.437Z"),
  "storageStats" : {
    "size" : 608500363,
    "count" : 1104369,
    "avgObjSize" : 550,
    "storageSize" : 352878592,
    "freeStorageSize" : 2490380,  // Starting in MongoDB 4.4
    "capped" : false,
    "wiredTiger" : {
      ...
    },
    "nindexes" : 2,
    "indexDetails" : {
      ...
    },
    "indexBuilds" : [
       "_id_1_abc_1"
    ],
    "totalIndexSize" : 260337664,
    "totalSize" : 613216256,    // Starting in MongoDB 4.4
    "indexSizes" : {
      "_id_" : 9891840,
      "_id_1_abc_1" : 250445824
    },
    "scaleFactor" : 1
  }
}

See Output for a reference on this document.有关本文档的参考信息，请参阅输出。

Performing $collStats with the storageStats option on a view results in an error.在视图上使用storageStats选项执行$collStats会导致错误。

count Field字段

The count field only exists in the output if you specify the count option.如果指定了count选项，则count字段仅存在于输出中。

For example, if you run $collStats with the count: {} option on a matrices collection:例如，如果在matrices集合上使用count: {}选项运行$collStats：

db.matrices.aggregate( [ { $collStats: { count: { } } } ] )

The query returns a result similar to the following:查询返回类似于以下内容的结果：

{
  "ns" : "test.matrices",
  "host" : mongo.example.net:27017",
  "localTime" : ISODate("2017-10-06T19:43:56.599Z"),
  "count" : 1103869
}

The total number of documents in the collection is also available as storageStats.count when storageStats: {} is specified. 指定storageStats:{}时，集合中的文档总数也可用作storageStats.count。For more information, see storageStats Document.有关更多信息，请参阅storageStats文档。

queryExecStats Document文档

The queryExecStats embedded document only exists in the output if you specify the queryExecStats option.只有在指定queryExecStats选项的情况下，queryExecStat嵌入文档才会存在于输出中。

The collectionScans field contains an embedded document bearing the following fields:collectionScans字段包含包含以下字段的嵌入文档：

For example, if you run $collStats with the queryExecStats: {} option on a matrices collection:例如，如果在矩阵集合上使用queryExecStats:{}选项运行$collStats：

db.matrices.aggregate( [ { $collStats: { queryExecStats: { } } } ] )

The query returns a result similar to the following:查询返回类似于以下内容的结果：

{
  "ns": "test.matrices",
  "host": "mongo.example.net:27017",
  "localTime": ISODate("2020-06-03T14:23:29.711Z"),
  "queryExecStats": {
      "collectionScans": {
          "total": NumberLong(33),
          "nonTailable": NumberLong(31)
      }
  }
}

$collStats on Sharded Collections分片集合上的$collStats

$collStats outputs one document per shard when run on sharded collections. 在分片集合上运行时，每个分片输出一个文档。Each output document contains a shard field with the name of the shard the document corresponds to.每个输出文档都包含一个shard字段，该字段具有文档所对应的分片的名称。

For example, if you run $collStats on a sharded collection with the count: {} option on a collection named matrices:例如，如果您在名为matrices的集合上使用count: {}选项对分片集合运行$collStats：

db.matrices.aggregate( [ { $collStats: { count: { } } } ] )

The query returns a result similar to the following:查询返回类似于以下内容的结果：

{
  "ns" : "test.matrices",
  "shard" : "s1",
  "host" : "s1-mongo1.example.net:27017",
  "localTime" : ISODate("2017-10-06T15:14:21.258Z"),
  "count" : 661705
}
{
  "ns" : "test.matrices",
  "shard" : "s2",
  "host" : "s2-mongo1.example.net:27017",
  "localTime" : ISODate("2017-10-06T15:14:21.258Z"),
  "count" : 442164
}