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Aggregation Pipelines

$collStats

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  • Syntax
  • Fields
  • Output
  • Examples
  • Errors

$collStats returns statistics for a given collection. $collstats must be the first stage in the aggregation pipeline. For more information, see $collStats. In Data Federation, $collStats can only be used to retrieve information about the partitions for a given collection or view.

Syntax

In Atlas Data Federation, $collStats accepts an empty document. It supports the optional field count only and returns an error if an unsupported option is specified.

db.<collection-name>|<view-name>.aggregate([{ "$collStats" : { "count" : {} } }])

Fields

Field
type
Description
Necessity
count
document
Adds the total number of documents in the partitions to the return document.
Optional

Output

$collStats returns the following fields in the document for each partition:

Field
Type
Description
count
number
The total number of documents in the partition. This is returned only if you specify the count option.
ns
string
The namespace of the current collection or view in the format [database].[collection|view].
partition
document
The details about the partition such as the source, format, size, and partition attributes, if any.
partition.format
string
The format of the file. Value can be any of the Supported Data Formats for data in a cloud store or MONGO for data in the Atlas cluster.
partition.attributes
document
The partition attributes for this partition defined in the path for cloud storage partitions. An empty document indicates that there are no partition attributes in the partition's data source.
partition.size
int
The size of the partition.
partition.source
string

The source for the partition. The value can be one of the following:

  • The path to the file on cloud storage.

  • The cluster name for partitions on Atlas.

partition.version
string

MongoDB version of the Atlas cluster. The $collStats stage returns this field only for Atlas cluster data stores. The value has the following format:

<major-version-number>.<minor-version-number>.<patch-version-number>

For example, 7.0.1.

Examples

The following example shows $collStats syntax for retrieving the partitions from a s3Db.abc collection with 3 files in a cloud storage federated database instance store:

use s3Db
db.abc.aggregate([ {$collStats: {}} ])

The preceding command returns the following output:

{ "ns" : "s3Db.abc", "partition" : { "format" : "JSON", "attributes" : { "year" : NumberLong(2018) }, "size" : 139, "source" : "s3://my-bucket/s3Db/abc/2018/1.json?delimiter=%2F&region=us-east-1" } }
{ "ns" : "s3Db.abc", "partition" : { "format" : "JSON", "attributes" : { "year" : NumberLong(2017) }, "size" : 124, "source" : "s3://my-bucket/s3Db/abc/2017/1.json?delimiter=%2F&region=us-east-1" } }
{ "ns" : "s3Db.abc", "partition" : { "format" : "JSON", "attributes" : { "year" : NumberLong(2017) }, "size" : 130, "source" : "s3://my-bucket/s3Db/abc/2017/2.json?delimiter=%2F&region=us-east-1" } }

The following example shows $collStats syntax for retrieving the partitions from the atlasDb.sampleColl collection in the Atlas cluster named mySandboxCluster:

use atlasDb
db.sampleColl.aggregate([ {$collStats: {}} ])

The preceding command returns the following output:

{ "ns" : "atlasDb.sampleColl", "partition" : { "format" : "MONGO", "attributes" : {  }, "size" : 94362191, "source" : "mySandboxCluster" } }

The following example shows $collStats syntax for retrieving the total number of documents in the partitions.

use s3Db
db.abc.aggregate([ {$collStats: {"count" : {} }} ])

The preceding command returns the following output:

{ "ns" : "atlasDb.sampleColl", "partition" : { "format" : "MONGO", "attributes" : {  }, "size" : 94362191, "source" : "mySandboxCluster" }, "count" : 23530}

Errors

An error similar to the following is returned if the collStats argument document contains any of the options allowed by the MongoDB server but not by Atlas Data Federation.

{
       "ok" : 0,
       "errmsg" : "$collStats param 'latencyStats' is not valid for Data Federation, correlationID = 1622929884a47d16f4888a1c",
       "code" : 9,
       "codeName" : "FailedToParse"
}

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