10000 Add step(), min() and max() in promql duration expressions by roidelapluie · Pull Request #16777 · prometheus/prometheus · GitHub
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Add step(), min() and max() in promql duration expressions #16777

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Add step(), min() and max() in promql duration expressions #16777

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@roidelapluie roidelapluie force-pushed the add-step-promql branch 5 times, most recently from 6253826 to ff7572c Compare June 26, 2025 12:00
@roidelapluie roidelapluie changed the title [WIP] Add step() in promql duration expressions Add step() in promql duration expressions Jun 26, 2025
@roidelapluie roidelapluie force-pushed the add-step-promql branch 3 times, most recently from b549206 to 140abe4 Compare June 26, 2025 12:50
@roidelapluie roidelapluie requested review from beorn7 and krajorama June 26, 2025 12:51
@roidelapluie roidelapluie marked this pull request as ready for review June 26, 2025 12:52
beorn7
beorn7 requested changes Jun 26, 2025
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Thanks for doing this.

@roidelapluie
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Thanks for doing this.

I have updated the PR with your comments.

@roidelapluie
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Funnily enough, rate [5m x 5m] was parsed correctly.

Fixed by this PR too.

@roidelapluie roidelapluie force-pushed the add-step-promql branch 3 times, most recently from 0eeced5 to 532e386 Compare June 27, 2025 09:04
@roidelapluie roidelapluie mentioned this pull request Jun 27, 2025
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darshanime
darshanime reviewed Jun 29, 2025
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docs/feature_flags.md
@@ -203,6 +205,10 @@ When using offset with duration expressions, you must wrap the expression in
parentheses. Without parentheses, only the first duration value will be used in
the offset calculation.

Additionally, `step()` can be used in duration expressions.
For a **range query**, it resolves to the step width of the range query.
For an **instant query**, it resolves to `0s`.
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can we also add a line or two about where step() might be useful? it won't be useful in selecting range window sizes for rate(), cmiiw?

aside: we recommend window size as being at least 4 times as large as the scrape interval, so would it make sense to introduce a scrape_interval() function to allow: rate(my_counter[4*scrape_interval()])?

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The issue is that we do not know the scrape interval for all the metrics. All jobs can be different, it can be overriden by target meta label, come from federation or recording rules.

krajorama
krajorama reviewed Jun 30, 2025
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Looks good, but I wonder if adding min/max was intentional?

If yes, please update PR description as well.

promql/parser/generated_parser.y
@@ -478,7 +479,7 @@ offset_expr: expr OFFSET offset_duration_expr
$$ = $1
}
| expr OFFSET error
{ yylex.(*parser).unexpected("offset", "number or duration"); $$ = $1 }
{ yylex.(*parser).unexpected("offset", "number, duration, or step()"); $$ = $1 }
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Suggested change
{ yylex.(*parser).unexpected("offset", "number, duration, or step()"); $$ = $1 }
{ yylex.(*parser).unexpected("offset", "number, duration or step()"); $$ = $1 }

promql/parser/generated_parser.y
@@ -574,11 +575,11 @@ subquery_expr : expr LEFT_BRACKET positive_duration_expr COLON positive_durati
| expr LEFT_BRACKET positive_duration_expr COLON positive_duration_expr error
{ yylex.(*parser).unexpected("subquery selector", "\"]\""); $$ = $1 }
| expr LEFT_BRACKET positive_duration_expr COLON error
{ yylex.(*parser).unexpected("subquery selector", "number or duration or \"]\""); $$ = $1 }
{ yylex.(*parser).unexpected("subquery selector", "number, duration, or step() or \"]\""); $$ = $1 }
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Suggested change
{ yylex.(*parser).unexpected("subquery selector", "number, duration, or step() or \"]\""); $$ = $1 }
{ yylex.(*parser).unexpected("subquery selector", "number, duration or step() or \"]\""); $$ = $1 }

promql/parser/generated_parser.y
| expr LEFT_BRACKET positive_duration_expr error
{ yylex.(*parser).unexpected("subquery or range", "\":\" or \"]\""); $$ = $1 }
| expr LEFT_BRACKET error
{ yylex.(*parser).unexpected("subquery selector", "number or duration"); $$ = $1 }
{ yylex.(*parser).unexpected("subquery or range selector", "number, duration, or step()"); $$ = $1 }
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Suggested change
{ yylex.(*parser).unexpected("subquery or range selector", "number, duration, or step()"); $$ = $1 }
{ yylex.(*parser).unexpected("subquery or range selector", "number, duration or step()"); $$ = $1 }

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IIRC we used the Oxford comma in Prometheus, did that change?

docs/feature_flags.md Outdated
@@ -203,6 +205,10 @@ When using offset with duration expressions, you must wrap the expression in
parentheses. Without parentheses, only the first duration value will be used in
the offset calculation.

Additionally, `step()` can be used in duration expressions.
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PR is also adding min and max operators, let's mention them here if it was intentional.

promql/durations_test.go
@@ -195,6 +195,24 @@ func TestCalculateDuration(t *testing.T) {
expected: -5 * time.Second,
allowedNegative: true,
},
{
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Missing tests for min, max operator.

promql/parser/parse_test.go
@@ -614,6 +614,43 @@ var testExpr = []struct {
fail: true,
errMsg: "1:11: parse error: unexpected <ignoring>",
},
// Vector selectors.
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Missing tests for min/max operator

@roidelapluie roidelapluie force-pushed the add-step-promql branch 3 times, most recently from 21885d5 to c4bdbb7 Compare June 30, 2025 14:51
@roidelapluie
Add step(), min(a,b) and max(a,b) in promql duration expressions
02cca53 
step() is a new keyword introduced to represent the query step width in duration expressions.

min(a,b) and max(a,b) return the min and max from two duration expressions.

Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>
@roidelapluie roidelapluie changed the title Add step() in promql duration expressions Add step(), min() and max() in promql duration expressions Jun 30, 2025
@roidelapluie roidelapluie requested a review from krajorama June 30, 2025 15:20
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@roidelapluie @beorn7 @darshanime @krajorama
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