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db.collection.latencyStats()

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db.collection.latencyStats(options)
Important
mongosh Method

This is a mongosh method. This is not the documentation for Node.js or other programming language specific driver methods.

In most cases, mongosh methods work the same way as the legacy mongo shell methods. However, some legacy methods are unavailable in mongosh.

For the legacy mongo shell documentation, refer to the documentation for the corresponding MongoDB Server release:

For MongoDB API drivers, refer to the language specific MongoDB driver documentation.

db.collection.latencyStats() returns latency statistics for a given collection. It is a wrapper around $collStats.

This method has the form:

db.collection.latencyStats( { histograms: <boolean> } )

The histograms argument is an optional boolean. If histograms: true then latencyStats() adds latency histograms to the return document.

Tip

latencyStats() returns a document containing a field latencyStats, containing the following fields:

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 upper values between 2048 microseconds and roughly 1 second, the histogram includes half-steps.

This field only exists given the latencyStats: { histograms: true } option. Empty ranges with a zero count are omitted from the output.

Each document bears the following fields:

Field Name
Description
micros

A 64-bit integer giving the inclusive upper time bound of the current latency range in microseconds.

The document's range spans between the previous document's micros value, exclusive, and this document's micros value, inclusive.

count
A 64-bit integer giving the number of operations with latency less than or equal to micros.

For example, if collStats returns the following histogram:

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) }
]

This indicates that there were:

  • 10 operations taking 1 microsecond or less,
  • 1 operation in the range (1, 2] microseconds,
  • 1 operation in the range (3072, 4096] microseconds,
  • 1000 operations in the range (12288, 16384], and
  • 100 operations in the range (32768, 49152].

You can run latencyStats() in mongosh as follows:

db.data.latencyStats( { histograms: true } ).pretty()

latencyStats() returns a document such as the following:

{
"ns" : "test.data",
"localTime" : ISODate("2016-11-01T21:56:28.962Z"),
"latencyStats" : {
"reads" : {
"histogram" : [
{
"micros" : NumberLong(16),
"count" : NumberLong(6)
},
{
"micros" : NumberLong(512),
"count" : NumberLong(1)
}
],
"latency" : NumberLong(747),
"ops" : NumberLong(7)
},
"writes" : {
"histogram" : [
{
"micros" : NumberLong(64),
"count" : NumberLong(1)
},
{
"micros" : NumberLong(24576),
"count" : NumberLong(1)
}
],
"latency" : NumberLong(26845),
"ops" : NumberLong(2)
},
"commands" : {
"histogram" : [ ],
"latency" : NumberLong(0),
"ops" : NumberLong(0)
}
}
}
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