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Fix serialization for empty ignoring() in combination with group_x()#17643

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juliusv merged 1 commit intomainfrom
fix-empty-ignoring-serialization
Dec 3, 2025
Merged

Fix serialization for empty ignoring() in combination with group_x()#17643
juliusv merged 1 commit intomainfrom
fix-empty-ignoring-serialization

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@juliusv
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@juliusv juliusv commented Dec 3, 2025

Currently both the backend and frontend printers/formatters/serializers incorrectly transform the following expression:

up * ignoring() group_left(__name__) node_boot_time_seconds

...into:

up * node_boot_time_seconds

...which yields a different result (including the metric name in the result vs. no metric name).

We need to keep empty ignoring() modifiers if there is a grouping modifier present.

Does this PR introduce a user-facing change?

[BUGFIX] PromQL: Fix serialization for empty `ignoring()` clause in combination with grouping modifiers

Currently both the backend and frontend printers/formatters/serializers
incorrectly transform the following expression:

```
up * ignoring() group_left(__name__) node_boot_time_seconds
```

...into:

```
up * node_boot_time_seconds
```

...which yields a different result (including the metric name in the result
vs. no metric name).

We need to keep empty `ignoring()` modifiers if there is a grouping modifier
present.

Signed-off-by: Julius Volz <julius.volz@gmail.com>
@juliusv juliusv requested a review from roidelapluie as a code owner December 3, 2025 13:18
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LGTM

@juliusv juliusv merged commit 22b3860 into main Dec 3, 2025
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@juliusv juliusv deleted the fix-empty-ignoring-serialization branch December 3, 2025 14:43
@bboreham
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For the release notes, how would an ordinary Prometheus user/admin know if they were affected by this bug?

@juliusv
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juliusv commented Dec 18, 2025

Not sure how to be succinct and simultaneously clear about it, but basically you were affected if you had an expression with empty ignoring() clause and simultaneous group_x() clause, AND:

  • ...tried to format it using the UI
  • ...tried to use the PromLens-style tree view with that expression
  • ...maybe some other use case where the code from printer.go was used?

In these cases, the expression would be formatted incorrectly (in display, but also in execution, when the result of the formatting was used to execute the query again) and the resulting query would probably have produced an evaluation error, since the entire ignoring() group_x() was stripped away, disallowing n:1 or 1:n matches.

@bboreham
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How about

[BUGFIX] PromQL: Fix possible corruption of PromQL text if the query had an empty `ignoring()` and non-empty grouping

@juliusv
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juliusv commented Dec 18, 2025

How about

[BUGFIX] PromQL: Fix possible corruption of PromQL text if the query had an empty `ignoring()` and non-empty grouping

Sounds good enough to me :)

renovate bot added a commit to sdwilsh/ansible-playbooks that referenced this pull request Jan 10, 2026
##### [\`v3.9.0\`](https://github.com/prometheus/prometheus/releases/tag/v3.9.0)

#### Note for users of Native Histograms

In version 3.9, Native Histograms is no longer experimental, and the feature flag `native-histogram` has no effect.  You must now turn on
the config setting `scrape_native_histograms` to collect Native Histogram samples from exporters.

#### Changelog

- \[CHANGE] Native Histograms are no longer experimental! Make the `native-histogram` feature flag a no-op. Use `scrape_native_histograms` config option instead. [#17528](prometheus/prometheus#17528)
- \[CHANGE] API: Add maximum limit of 10,000 sets of statistics to TSDB status endpoint. [#17647](prometheus/prometheus#17647)
- \[FEATURE] API: Add /api/v1/features for clients to understand which features are supported. [#17427](prometheus/prometheus#17427)
- \[FEATURE] Promtool: Add `start_timestamp` field for unit tests. [#17636](prometheus/prometheus#17636)
- \[FEATURE] Promtool: Add `--format seriesjson` option to `tsdb dump` to output just series labels in JSON format. [#13409](prometheus/prometheus#13409)
- \[FEATURE] Add `--storage.tsdb.delay-compact-file.path` flag for better interoperability with Thanos. [#17435](prometheus/prometheus#17435)
- \[FEATURE] UI: Add an option on the query drop-down menu to duplicate that query panel. [#17714](prometheus/prometheus#17714)
- \[ENHANCEMENT]: TSDB: add flag `--storage.tsdb.block-reload-interval` to configure TSDB Block Reload Interval. [#16728](prometheus/prometheus#16728)
- \[ENHANCEMENT] UI: Add graph option to start the chart's Y axis at zero. [#17565](prometheus/prometheus#17565)
- \[ENHANCEMENT] Scraping: Classic protobuf format no longer requires the unit in the metric name. [#16834](prometheus/prometheus#16834)
- \[ENHANCEMENT] PromQL, Rules, SD, Scraping: Add native histograms to complement existing summaries. [#17374](prometheus/prometheus#17374)
- \[ENHANCEMENT] Notifications: Add a histogram `prometheus_notifications_latency_histogram_seconds` to complement the existing summary. [#16637](prometheus/prometheus#16637)
- \[ENHANCEMENT] Remote-write: Add custom scope support for AzureAD authentication. [#17483](prometheus/prometheus#17483)
- \[ENHANCEMENT] SD: add a `config` label with job name for most `prometheus_sd_refresh` metrics. [#17138](prometheus/prometheus#17138)
- \[ENHANCEMENT] TSDB: New histogram `prometheus_tsdb_sample_ooo_delta`, the distribution of out-of-order samples in seconds. Collected for all samples, accepted or not. [#17477](prometheus/prometheus#17477)
- \[ENHANCEMENT] Remote-read: Validate histograms received via remote-read. [#17561](prometheus/prometheus#17561)
- \[PERF] TSDB: Small optimizations to postings index. [#17439](prometheus/prometheus#17439)
- \[PERF] Scraping: Speed up relabelling of series. [#17530](prometheus/prometheus#17530)
- \[PERF] PromQL: Small optimisations in binary operators. [#17524](prometheus/prometheus#17524), [#17519](prometheus/prometheus#17519).
- \[BUGFIX] UI: PromQL autocomplete now shows the correct type and HELP text for OpenMetrics counters whose samples end in `_total`. [#17682](prometheus/prometheus#17682)
- \[BUGFIX] UI: Fixed codemirror-promql incorrectly showing label completion suggestions after the closing curly brace of a vector selector. [#17602](prometheus/prometheus#17602)
- \[BUGFIX] UI: Query editor no longer suggests a duration unit if one is already present after a number. [#17605](prometheus/prometheus#17605)
- \[BUGFIX] PromQL: Fix some "vector cannot contain metrics with the same labelset" errors when experimental delayed name removal is enabled. [#17678](prometheus/prometheus#17678)
- \[BUGFIX] PromQL: Fix possible corruption of PromQL text if the query had an empty `ignoring()` and non-empty grouping. [#17643](prometheus/prometheus#17643)
- \[BUGFIX] PromQL: Fix resets/changes to return empty results for anchored selectors when all samples are outside the range. [#17479](prometheus/prometheus#17479)
- \[BUGFIX] PromQL: Check more consistently for many-to-one matching in filter binary operators. [#17668](prometheus/prometheus#17668)
- \[BUGFIX] PromQL: Fix collision in unary negation with non-overlapping series. [#17708](prometheus/prometheus#17708)
- \[BUGFIX] PromQL: Fix collision in label\_join and label\_replace with non-overlapping series. [#17703](prometheus/prometheus#17703)
- \[BUGFIX] PromQL: Fix bug with inconsistent results for queries with OR expression when experimental delayed name removal is enabled. [#17161](prometheus/prometheus#17161)
- \[BUGFIX] PromQL: Ensure that `rate`/`increase`/`delta` of histograms results in a gauge histogram. [#17608](prometheus/prometheus#17608)
- \[BUGFIX] PromQL: Do not panic while iterating over invalid histograms. [#17559](prometheus/prometheus#17559)
- \[BUGFIX] TSDB: Reject chunk files whose encoded chunk length overflows int. [#17533](prometheus/prometheus#17533)
- \[BUGFIX] TSDB: Do not panic during resolution reduction of invalid histograms. [#17561](prometheus/prometheus#17561)
- \[BUGFIX] Remote-write Receive: Avoid duplicate labels when experimental type-and-unit-label feature is enabled. [#17546](prometheus/prometheus#17546)
- \[BUGFIX] OTLP Receiver: Only write metadata to disk when experimental metadata-wal-records feature is enabled. [#17472](prometheus/prometheus#17472)
renovate bot added a commit to sdwilsh/ansible-playbooks that referenced this pull request Jan 10, 2026
##### [\`v3.9.1\`](https://github.com/prometheus/prometheus/releases/tag/v3.9.1)

- \[BUGFIX] Agent: fix crash shortly after startup from invalid type of object. [#17802](prometheus/prometheus#17802)
- \[BUGFIX] Scraping: fix relabel keep/drop not working. [#17807](prometheus/prometheus#17807)

---
##### [\`v3.9.0\`](https://github.com/prometheus/prometheus/releases/tag/v3.9.0)

#### Note for users of Native Histograms

In version 3.9, Native Histograms is no longer experimental, and the feature flag `native-histogram` has no effect.  You must now turn on
the config setting `scrape_native_histograms` to collect Native Histogram samples from exporters.

#### Changelog

- \[CHANGE] Native Histograms are no longer experimental! Make the `native-histogram` feature flag a no-op. Use `scrape_native_histograms` config option instead. [#17528](prometheus/prometheus#17528)
- \[CHANGE] API: Add maximum limit of 10,000 sets of statistics to TSDB status endpoint. [#17647](prometheus/prometheus#17647)
- \[FEATURE] API: Add /api/v1/features for clients to understand which features are supported. [#17427](prometheus/prometheus#17427)
- \[FEATURE] Promtool: Add `start_timestamp` field for unit tests. [#17636](prometheus/prometheus#17636)
- \[FEATURE] Promtool: Add `--format seriesjson` option to `tsdb dump` to output just series labels in JSON format. [#13409](prometheus/prometheus#13409)
- \[FEATURE] Add `--storage.tsdb.delay-compact-file.path` flag for better interoperability with Thanos. [#17435](prometheus/prometheus#17435)
- \[FEATURE] UI: Add an option on the query drop-down menu to duplicate that query panel. [#17714](prometheus/prometheus#17714)
- \[ENHANCEMENT]: TSDB: add flag `--storage.tsdb.block-reload-interval` to configure TSDB Block Reload Interval. [#16728](prometheus/prometheus#16728)
- \[ENHANCEMENT] UI: Add graph option to start the chart's Y axis at zero. [#17565](prometheus/prometheus#17565)
- \[ENHANCEMENT] Scraping: Classic protobuf format no longer requires the unit in the metric name. [#16834](prometheus/prometheus#16834)
- \[ENHANCEMENT] PromQL, Rules, SD, Scraping: Add native histograms to complement existing summaries. [#17374](prometheus/prometheus#17374)
- \[ENHANCEMENT] Notifications: Add a histogram `prometheus_notifications_latency_histogram_seconds` to complement the existing summary. [#16637](prometheus/prometheus#16637)
- \[ENHANCEMENT] Remote-write: Add custom scope support for AzureAD authentication. [#17483](prometheus/prometheus#17483)
- \[ENHANCEMENT] SD: add a `config` label with job name for most `prometheus_sd_refresh` metrics. [#17138](prometheus/prometheus#17138)
- \[ENHANCEMENT] TSDB: New histogram `prometheus_tsdb_sample_ooo_delta`, the distribution of out-of-order samples in seconds. Collected for all samples, accepted or not. [#17477](prometheus/prometheus#17477)
- \[ENHANCEMENT] Remote-read: Validate histograms received via remote-read. [#17561](prometheus/prometheus#17561)
- \[PERF] TSDB: Small optimizations to postings index. [#17439](prometheus/prometheus#17439)
- \[PERF] Scraping: Speed up relabelling of series. [#17530](prometheus/prometheus#17530)
- \[PERF] PromQL: Small optimisations in binary operators. [#17524](prometheus/prometheus#17524), [#17519](prometheus/prometheus#17519).
- \[BUGFIX] UI: PromQL autocomplete now shows the correct type and HELP text for OpenMetrics counters whose samples end in `_total`. [#17682](prometheus/prometheus#17682)
- \[BUGFIX] UI: Fixed codemirror-promql incorrectly showing label completion suggestions after the closing curly brace of a vector selector. [#17602](prometheus/prometheus#17602)
- \[BUGFIX] UI: Query editor no longer suggests a duration unit if one is already present after a number. [#17605](prometheus/prometheus#17605)
- \[BUGFIX] PromQL: Fix some "vector cannot contain metrics with the same labelset" errors when experimental delayed name removal is enabled. [#17678](prometheus/prometheus#17678)
- \[BUGFIX] PromQL: Fix possible corruption of PromQL text if the query had an empty `ignoring()` and non-empty grouping. [#17643](prometheus/prometheus#17643)
- \[BUGFIX] PromQL: Fix resets/changes to return empty results for anchored selectors when all samples are outside the range. [#17479](prometheus/prometheus#17479)
- \[BUGFIX] PromQL: Check more consistently for many-to-one matching in filter binary operators. [#17668](prometheus/prometheus#17668)
- \[BUGFIX] PromQL: Fix collision in unary negation with non-overlapping series. [#17708](prometheus/prometheus#17708)
- \[BUGFIX] PromQL: Fix collision in label\_join and label\_replace with non-overlapping series. [#17703](prometheus/prometheus#17703)
- \[BUGFIX] PromQL: Fix bug with inconsistent results for queries with OR expression when experimental delayed name removal is enabled. [#17161](prometheus/prometheus#17161)
- \[BUGFIX] PromQL: Ensure that `rate`/`increase`/`delta` of histograms results in a gauge histogram. [#17608](prometheus/prometheus#17608)
- \[BUGFIX] PromQL: Do not panic while iterating over invalid histograms. [#17559](prometheus/prometheus#17559)
- \[BUGFIX] TSDB: Reject chunk files whose encoded chunk length overflows int. [#17533](prometheus/prometheus#17533)
- \[BUGFIX] TSDB: Do not panic during resolution reduction of invalid histograms. [#17561](prometheus/prometheus#17561)
- \[BUGFIX] Remote-write Receive: Avoid duplicate labels when experimental type-and-unit-label feature is enabled. [#17546](prometheus/prometheus#17546)
- \[BUGFIX] OTLP Receiver: Only write metadata to disk when experimental metadata-wal-records feature is enabled. [#17472](prometheus/prometheus#17472)
renovate bot added a commit to sdwilsh/ansible-playbooks that referenced this pull request Jan 10, 2026
##### [\`v3.9.1\`](https://github.com/prometheus/prometheus/releases/tag/v3.9.1)

- \[BUGFIX] Agent: fix crash shortly after startup from invalid type of object. [#17802](prometheus/prometheus#17802)
- \[BUGFIX] Scraping: fix relabel keep/drop not working. [#17807](prometheus/prometheus#17807)

---
##### [\`v3.9.0\`](https://github.com/prometheus/prometheus/releases/tag/v3.9.0)

#### Note for users of Native Histograms

In version 3.9, Native Histograms is no longer experimental, and the feature flag `native-histogram` has no effect.  You must now turn on
the config setting `scrape_native_histograms` to collect Native Histogram samples from exporters.

#### Changelog

- \[CHANGE] Native Histograms are no longer experimental! Make the `native-histogram` feature flag a no-op. Use `scrape_native_histograms` config option instead. [#17528](prometheus/prometheus#17528)
- \[CHANGE] API: Add maximum limit of 10,000 sets of statistics to TSDB status endpoint. [#17647](prometheus/prometheus#17647)
- \[FEATURE] API: Add /api/v1/features for clients to understand which features are supported. [#17427](prometheus/prometheus#17427)
- \[FEATURE] Promtool: Add `start_timestamp` field for unit tests. [#17636](prometheus/prometheus#17636)
- \[FEATURE] Promtool: Add `--format seriesjson` option to `tsdb dump` to output just series labels in JSON format. [#13409](prometheus/prometheus#13409)
- \[FEATURE] Add `--storage.tsdb.delay-compact-file.path` flag for better interoperability with Thanos. [#17435](prometheus/prometheus#17435)
- \[FEATURE] UI: Add an option on the query drop-down menu to duplicate that query panel. [#17714](prometheus/prometheus#17714)
- \[ENHANCEMENT]: TSDB: add flag `--storage.tsdb.block-reload-interval` to configure TSDB Block Reload Interval. [#16728](prometheus/prometheus#16728)
- \[ENHANCEMENT] UI: Add graph option to start the chart's Y axis at zero. [#17565](prometheus/prometheus#17565)
- \[ENHANCEMENT] Scraping: Classic protobuf format no longer requires the unit in the metric name. [#16834](prometheus/prometheus#16834)
- \[ENHANCEMENT] PromQL, Rules, SD, Scraping: Add native histograms to complement existing summaries. [#17374](prometheus/prometheus#17374)
- \[ENHANCEMENT] Notifications: Add a histogram `prometheus_notifications_latency_histogram_seconds` to complement the existing summary. [#16637](prometheus/prometheus#16637)
- \[ENHANCEMENT] Remote-write: Add custom scope support for AzureAD authentication. [#17483](prometheus/prometheus#17483)
- \[ENHANCEMENT] SD: add a `config` label with job name for most `prometheus_sd_refresh` metrics. [#17138](prometheus/prometheus#17138)
- \[ENHANCEMENT] TSDB: New histogram `prometheus_tsdb_sample_ooo_delta`, the distribution of out-of-order samples in seconds. Collected for all samples, accepted or not. [#17477](prometheus/prometheus#17477)
- \[ENHANCEMENT] Remote-read: Validate histograms received via remote-read. [#17561](prometheus/prometheus#17561)
- \[PERF] TSDB: Small optimizations to postings index. [#17439](prometheus/prometheus#17439)
- \[PERF] Scraping: Speed up relabelling of series. [#17530](prometheus/prometheus#17530)
- \[PERF] PromQL: Small optimisations in binary operators. [#17524](prometheus/prometheus#17524), [#17519](prometheus/prometheus#17519).
- \[BUGFIX] UI: PromQL autocomplete now shows the correct type and HELP text for OpenMetrics counters whose samples end in `_total`. [#17682](prometheus/prometheus#17682)
- \[BUGFIX] UI: Fixed codemirror-promql incorrectly showing label completion suggestions after the closing curly brace of a vector selector. [#17602](prometheus/prometheus#17602)
- \[BUGFIX] UI: Query editor no longer suggests a duration unit if one is already present after a number. [#17605](prometheus/prometheus#17605)
- \[BUGFIX] PromQL: Fix some "vector cannot contain metrics with the same labelset" errors when experimental delayed name removal is enabled. [#17678](prometheus/prometheus#17678)
- \[BUGFIX] PromQL: Fix possible corruption of PromQL text if the query had an empty `ignoring()` and non-empty grouping. [#17643](prometheus/prometheus#17643)
- \[BUGFIX] PromQL: Fix resets/changes to return empty results for anchored selectors when all samples are outside the range. [#17479](prometheus/prometheus#17479)
- \[BUGFIX] PromQL: Check more consistently for many-to-one matching in filter binary operators. [#17668](prometheus/prometheus#17668)
- \[BUGFIX] PromQL: Fix collision in unary negation with non-overlapping series. [#17708](prometheus/prometheus#17708)
- \[BUGFIX] PromQL: Fix collision in label\_join and label\_replace with non-overlapping series. [#17703](prometheus/prometheus#17703)
- \[BUGFIX] PromQL: Fix bug with inconsistent results for queries with OR expression when experimental delayed name removal is enabled. [#17161](prometheus/prometheus#17161)
- \[BUGFIX] PromQL: Ensure that `rate`/`increase`/`delta` of histograms results in a gauge histogram. [#17608](prometheus/prometheus#17608)
- \[BUGFIX] PromQL: Do not panic while iterating over invalid histograms. [#17559](prometheus/prometheus#17559)
- \[BUGFIX] TSDB: Reject chunk files whose encoded chunk length overflows int. [#17533](prometheus/prometheus#17533)
- \[BUGFIX] TSDB: Do not panic during resolution reduction of invalid histograms. [#17561](prometheus/prometheus#17561)
- \[BUGFIX] Remote-write Receive: Avoid duplicate labels when experimental type-and-unit-label feature is enabled. [#17546](prometheus/prometheus#17546)
- \[BUGFIX] OTLP Receiver: Only write metadata to disk when experimental metadata-wal-records feature is enabled. [#17472](prometheus/prometheus#17472)
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