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Grafana LokiLogQL

LogQL: Log query language

LogQL is Grafana Loki’s PromQL-inspired query language. Queries act as if they are a distributed grep to aggregate log sources. LogQL uses labels and operators for filtering.

There are two types of LogQL queries:

Binary operators

Arithmetic operators

The following binary arithmetic operators exist in Loki:

  • + (addition)
  • - (subtraction)
  • * (multiplication)
  • / (division)
  • % (modulo)
  • ^ (power/exponentiation)

Binary arithmetic operators are defined between two literals (scalars), a literal and a vector, and two vectors.

Between two literals, the behavior is obvious: They evaluate to another literal that is the result of the operator applied to both scalar operands (1 + 1 = 2).

Between a vector and a literal, the operator is applied to the value of every data sample in the vector, e.g. if a time series vector is multiplied by 2, the result is another vector in which every sample value of the original vector is multiplied by 2.

Between two vectors, a binary arithmetic operator is applied to each entry in the left-hand side vector and its matching element in the right-hand vector. The result is propagated into the result vector with the grouping labels becoming the output label set. Entries for which no matching entry in the right-hand vector can be found are not part of the result.

Pay special attention to operator order when chaining arithmetic operators.

Arithmetic Examples

Implement a health check with a simple query:

1 + 1

Double the rate of a a log stream’s entries:

sum(rate({app="foo"})) * 2

Get proportion of warning logs to error logs for the foo app

sum(rate({app="foo", level="warn"}[1m])) / sum(rate({app="foo", level="error"}[1m]))

Logical and set operators

These logical/set binary operators are only defined between two vectors:

  • and (intersection)
  • or (union)
  • unless (complement)

vector1 and vector2 results in a vector consisting of the elements of vector1 for which there are elements in vector2 with exactly matching label sets. Other elements are dropped.

vector1 or vector2 results in a vector that contains all original elements (label sets + values) of vector1 and additionally all elements of vector2 which do not have matching label sets in vector1.

vector1 unless vector2 results in a vector consisting of the elements of vector1 for which there are no elements in vector2 with exactly matching label sets. All matching elements in both vectors are dropped.

Binary operators examples

This contrived query will return the intersection of these queries, effectively rate({app="bar"}):

rate({app=~"foo|bar"}[1m]) and rate({app="bar"}[1m])

Comparison operators

  • == (equality)
  • != (inequality)
  • > (greater than)
  • >= (greater than or equal to)
  • < (less than)
  • <= (less than or equal to)

Comparison operators are defined between scalar/scalar, vector/scalar, and vector/vector value pairs. By default they filter. Their behavior can be modified by providing bool after the operator, which will return 0 or 1 for the value rather than filtering.

Between two scalars, these operators result in another scalar that is either 0 (false) or 1 (true), depending on the comparison result. The bool modifier must not be provided.

1 >= 1 is equivalent to 1

Between a vector and a scalar, these operators are applied to the value of every data sample in the vector, and vector elements between which the comparison result is false get dropped from the result vector. If the bool modifier is provided, vector elements that would be dropped instead have the value 0 and vector elements that would be kept have the value 1.

Filters the streams which logged at least 10 lines in the last minute:

count_over_time({foo="bar"}[1m]) > 10

Attach the value(s) 0/1 to streams that logged less/more than 10 lines:

count_over_time({foo="bar"}[1m]) > bool 10

Between two vectors, these operators behave as a filter by default, applied to matching entries. Vector elements for which the expression is not true or which do not find a match on the other side of the expression get dropped from the result, while the others are propagated into a result vector. If the bool modifier is provided, vector elements that would have been dropped instead have the value 0 and vector elements that would be kept have the value 1, with the grouping labels again becoming the output label set.

Return the streams matching app=foo without app labels that have higher counts within the last minute than their counterparts matching app=bar without app labels:

sum without(app) (count_over_time({app="foo"}[1m])) > sum without(app) (count_over_time({app="bar"}[1m]))

Same as above, but vectors have their values set to 1 if they pass the comparison or 0 if they fail/would otherwise have been filtered out:

sum without(app) (count_over_time({app="foo"}[1m])) > bool sum without(app) (count_over_time({app="bar"}[1m]))

Order of operations

When chaining or combining operators, you have to consider operator precedence: Generally, you can assume regular mathematical convention with operators on the same precedence level being left-associative.

More details can be found in the Golang language documentation.

1 + 2 / 3 is equal to 1 + ( 2 / 3 ).

2 * 3 % 2 is evaluated as (2 * 3) % 2.

Keywords on and ignoring

The ignoring keyword causes specified labels to be ignored during matching. The syntax:

<vector expr> <bin-op> ignoring(<labels>) <vector expr>

This example will return the machines which total count within the last minutes exceed average value for app foo.

max by(machine) (count_over_time({app="foo"}[1m])) > bool ignoring(machine) avg(count_over_time({app="foo"}[1m]))

The on keyword reduces the set of considered labels to a specified list. The syntax:

<vector expr> <bin-op> on(<labels>) <vector expr>

This example will return every machine total count within the last minutes ratio in app foo:

sum by(machine) (count_over_time({app="foo"}[1m])) / on() sum(count_over_time({app="foo"}[1m]))

Many-to-one and one-to-many vector matches

Many-to-one and one-to-many matchings occur when each vector element on the “one”-side can match with multiple elements on the “many”-side. You must explicitly request matching by using the group_left or group_right modifier, where left or right determines which vector has the higher cardinality. The syntax:

<vector expr> <bin-op> ignoring(<labels>) group_left(<labels>) <vector expr>
<vector expr> <bin-op> ignoring(<labels>) group_right(<labels>) <vector expr>
<vector expr> <bin-op> on(<labels>) group_left(<labels>) <vector expr>
<vector expr> <bin-op> on(<labels>) group_right(<labels>) <vector expr>

The label list provided with the group modifier contains additional labels from the “one”-side that are included in the result metrics. And a label should only appear in one of the lists specified by on and group_x. Every time series of the result vector must be uniquely identifiable. Grouping modifiers can only be used for comparison and arithmetic. By default, the system matches and, unless, and or operations with all entries in the right vector.

The following example returns the rates requests partitioned by app and status as a percentage of total requests.

sum by (app, status) (
  rate(
    {job="http-server"}
      | json
      [5m]
  )
)
/ on (app) group_left
sum by (app) (
  rate(
    {job="http-server"}
      | json
      [5m]
  )
)

=>
[
  {app="foo", status="200"} => 0.8
  {app="foo", status="400"} => 0.1
  {app="foo", status="500"} => 0.1
]

This version uses group_left(<labels>) to include <labels> from the right hand side in the result and returns the cost of discarded events per user, organization, and namespace:

sum by (user, namespace) (
  rate(
    {job="events"}
      | logfmt
      | discarded="true"
      [5m]
  )
)
* on (user) group_left(organization)
max_over_time(
  {job="cost-calculator"}
    | logfmt
    | unwrap cost
    [5m]
) by (user, organization)

=>
[
  {user="foo", namespace="dev", organization="little-org"} => 10
  {user="foo", namespace="prod", organization="little-org"} => 50
  {user="bar", namespace="dev", organization="big-org"} => 70
  {user="bar", namespace="prod", organization="big-org"} => 200
]

Comments

LogQL queries can be commented using the # character:

{app="foo"} # anything that comes after will not be interpreted in your query

With multi-line LogQL queries, the query parser can exclude whole or partial lines using #:

{app="foo"}
    | json
    # this line will be ignored
    | bar="baz" # this checks if bar = "baz"

Pipeline Errors

There are multiple reasons which cause pipeline processing errors, such as:

  • A numeric label filter may fail to turn a label value into a number
  • A metric conversion for a label may fail.
  • A log line is not a valid json document.
  • etc…

When those failures happen, Loki won’t filter out those log lines. Instead they are passed into the next stage of the pipeline with a new system label named __error__. The only way to filter out errors is by using a label filter expressions. The __error__ label can’t be renamed via the language.

For example to remove json errors:

  {cluster="ops-tools1",container="ingress-nginx"}
    | json
    | __error__ != "JSONParserErr"

Alternatively you can remove all error using a catch all matcher such as __error__ = "" or even show only errors using __error__ != "".

The filter should be placed after the stage that generated this error. This means if you need to remove errors from an unwrap expression it needs to be placed after the unwrap.

quantile_over_time(
	0.99,
	{container="ingress-nginx",service="hosted-grafana"}
	| json
	| unwrap response_latency_seconds
	| __error__=""[1m]
	) by (cluster)

Metric queries cannot contains errors, in case errors are found during execution, Loki will return an error and appropriate status code.

Functions

Loki supports functions to operate on data.

label_replace()

For each timeseries in v,

label_replace(v instant-vector,
    dst_label string,
    replacement string,
    src_label string,
    regex string)

matches the regular expression regex against the label src_label. If it matches, then the timeseries is returned with the label dst_label replaced by the expansion of replacement.

$1 is replaced with the first matching subgroup, $2 with the second etc. If the regular expression doesn’t match, then the timeseries is returned unchanged.

This example will return a vector with each time series having a foo label with the value a added to it:

label_replace(rate({job="api-server",service="a:c"} |= "err" [1m]), "foo", "$1",
  "service", "(.*):.*")