$collStats (aggregation)
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Definition
$collStats
Returns statistics regarding a collection or view.
The
$collStats
stage has the following prototype form:{ $collStats: { latencyStats: { histograms: <boolean> }, storageStats: { scale: <number> }, count: {}, queryExecStats: {} } } The
$collStats
stage accepts an argument document with the following optional fields:Field NameDescriptionlatencyStats
Adds latency statistics to the return document.latencyStats.histograms
Adds latency histogram information to the embedded documents inlatencyStats
iftrue
.storageStats
Adds storage statistics to the return document.
Specify an empty document (i.e.
storageStats: {}
) to use the default scale factor of 1 for the various size data. Scale factor of 1 displays the returned sizes in bytes.Specify the scale factor (i.e.
storageStats: { scale: <number> }
) to use the specified scale factor for the various size data. For example, to display kilobytes rather than bytes, specify a scale value of 1024.If you specify a non-integer scale factor, MongoDB uses the integer part of the specified factor. For example, if you specify a scale factor of
1023.999
, MongoDB uses1023
as the scale factor.The scale factor does not affect those sizes that specify the unit of measurement in the field name, such as
"bytes currently in the cache"
.
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
FieldqueryExecStats
Adds query execution statistics to the return document.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 NameDescriptionns
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.host
The hostname and port of themongod
process which produced the output document.localTime
The current time on the MongoDB server, expressed as UTC milliseconds since the UNIX epoch.latencyStats
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
Statistics related to a collection's storage engine. See
storageStats
Document for details on this document.The various size data is scaled by the specified factor (with the exception of those sizes that specify the unit of measurement in the field name).
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.queryExecStats
Statistics related to query execution for the collection.
Only present when the
queryExecStats: {}
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 64-bit integer giving the total combined
latency in microseconds. | |||||||||||||
ops | A 64-bit integer 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 lower 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:
|
[1] |
|
For example, if you run $collStats
with the latencyStats: {}
option
on a matrices
collection:
db.matrices.aggregate( [ { $collStats: { latencyStats: { histograms: true } } } ] )
This query returns a result similar to the following:
{ "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
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:
db.matrices.aggregate( [ { $collStats: { storageStats: { } } } ] )
This query returns a result similar to the following:
{ "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, "capped" : false, "wiredTiger" : { ... }, "nindexes" : 2, "indexDetails" : { ... }, "indexBuilds" : [ // Starting in MongoDB 4.2 "_id_1_abc_1" ], "totalIndexSize" : 260337664, "totalSize" : 613216256, "indexSizes" : { "_id_" : 9891840, "_id_1_abc_1" : 250445824 }, "scaleFactor" : 1 // Starting in MongoDB 4.2 } }
See Output for a reference on this document.
Note
In-progress Indexes
Starting in MongoDB 4.2, the returned storageStats
includes
information on indexes being built. For details, see:
Performing $collStats
with the storageStats
option on a
view results in an error.
count
Field
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:
db.matrices.aggregate( [ { $collStats: { count: { } } } ] )
The query returns a result similar to the following:
{ "ns" : "test.matrices", "host" : mongo.example.net:27017", "localTime" : ISODate("2017-10-06T19:43:56.599Z"), "count" : 1103869 }
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.
queryExecStats
Document
The queryExecStats
embedded document only exists in the output if
you specify the queryExecStats
option.
The collectionScans
field contains an embedded document bearing the
following fields:
Field Name | Description |
---|---|
total | A 64-bit integer giving the total number of queries that
performed a collection scan. The total consists of queries that
did and did not use a tailable cursor. |
nonTailable | A 64-bit integer giving the number of queries that performed a
collection scan that did not use a tailable cursor. |
For example, if you run $collStats
with the queryExecStats: {}
option on a matrices
collection:
db.matrices.aggregate( [ { $collStats: { queryExecStats: { } } } ] )
The query returns a result similar to the following:
{ "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
$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
:
db.matrices.aggregate( [ { $collStats: { count: { } } } ] )
The query returns a result similar to the following:
{ "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 }