- Reference >
- Operators >
- Aggregation Pipeline Stages >
- $collStats (aggregation)
$collStats (aggregation)¶
On this page
Definition¶
-
$collStats
¶ New in version 3.4.
Returns statistics regarding a collection or view.
The
$collStats
stage has the following prototype form:The
$collStats
stage accepts an argument document with the following optional fields:Field Name Description latencyStats
Adds latency statistics to the return document. latencyStats.histograms
Adds latency histogram information to the embedded documents in latencyStats
iftrue
.storageStats
Adds storage statistics to the return document. count
Adds the total number of documents in the collection to the return document.
Note
The count is based on the collection’s metadata, which provides a fast but sometimes inaccurate count for sharded clusters.
See count Field
New in version 3.6.
For a collection in a replica set or a non-sharded collection in a cluster,
$collStats
outputs a single document. For a sharded collection,$collStats
outputs one document per shard. The output document includes the following fields:Field Name Description ns
The namespace of the requested collection or view. shard
The name of the shard the output document corresponds to.
Only present when
$collStats
runs on a sharded cluster. Both sharded and non-sharded collections will produce this field.New in version 3.6.
host
The hostname and port of the mongod process which produced the output document.
New in version 3.6.
localTime
The current time on the MongoDB server, expressed as UTC milliseconds since the Unix epoch. latencyStats
A collection of statistics related to request latency for a collection or view. See latencyStats Document for details on this document.
Only present when the
latencyStats: {}
option is specified.storageStats
A collection of statistics related to a collection’s storage engine. See storageStats Document for details on this document.
Only present when the
storageStats: {}
option is specified. Returns an error if applied to a view.count
The total number of documents in the collection. This data is also available in
storageStats.count
.Note
The count is based on the collection’s metadata, which provides a fast but sometimes inaccurate count for sharded clusters.
Only present when the
count: {}
option is specified. Returns an error if applied to a view.
Behavior¶
$collStats
must be the first stage in an aggregation pipeline, or
else the pipeline returns an error.
Transactions¶
$collStats
is not allowed in transactions.
latencyStats
Document¶
The latencyStats
embedded document only exists in the output if
you specify the latencyStats
option.
Field Name | Description |
---|---|
reads |
Latency statistics for read requests. |
writes |
Latency statistics for write requests. |
commands |
Latency statistics for database commands. |
Each of these fields contains an embedded document bearing the following fields:
Field Name | Description | ||||||
---|---|---|---|---|---|---|---|
latency |
A long giving the total combined
latency in microseconds. |
||||||
ops |
A long giving the total number of
operations performed on the collection since startup. |
||||||
histogram |
An array of embedded documents, each representing a latency range. Each document covers twice the previous document’s range. For upper values between 2048 microseconds and roughly 1 second, the histogram includes half-steps. This field only exists given the
Each document bears the following fields:
For example, if This indicates that there were:
|
For example, if you run $collStats
with the latencyStats: {}
option
on a matrices
collection:
This query returns a result similar to the following:
storageStats
Document¶
The storageStats
embedded document only exists in the output if you
specify the storageStats
option.
The contents of this document are dependent on the storage engine in use. See Output for a reference on this document.
For example, if you run $collStats
with the storageStats: {}
option on a matrices
collection using the WiredTiger Storage Engine:
This query returns a result similar to the following:
Performing $collStats
with the storageStats
option on a
view results in an error.
count
Field¶
New in version 3.6.
The count
field only exists in the output if you specify the
count
option.
For example, if you run $collStats
with the count: {}
option on
a matrices
collection:
The query returns a result similar to the following:
Note
The count is based on the collection’s metadata, which provides a fast but sometimes inaccurate count for sharded clusters.
The total number of documents in the collection is also available as
storageStats.count
when storageStats: {}
is specified. For more
information, see storageStats Document.
$collStats
on Sharded Collections¶
$collStats
outputs one document per shard when run on
sharded collections. Each
output document contains a shard
field with the name of the shard
the document corresponds to.
For example, if you run $collStats
on a sharded collection with the
count: {}
option on a collection named matrices
:
The query returns a result similar to the following:
See also