2.15 release notes (#10165)

docs/sources/mimir/release-notes/v2.15.md

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+---
+title: "Grafana Mimir version 2.15 release notes"
+menuTitle: "V2.15 release notes"
+description: "Release notes for Grafana Mimir version 2.15"
+weight: 1100
+---
+
+# Grafana Mimir version 2.15 release notes
+
+<!-- vale Grafana.GoogleWill = NO -->
+<!-- vale Grafana.Timeless = NO -->
+<!-- Release notes are often future focused -->
+
+Grafana Labs is excited to announce version 2.15 of Grafana Mimir.
+
+The highlights that follow include the top features, enhancements, and bug fixes in this release.
+For the complete list of changes, refer to the [CHANGELOG](https://github.com/grafana/mimir/blob/main/CHANGELOG.md).
+
+## Features and enhancements
+
+S2 compression for gRPC is now supported using the following flags:
+
+- `-alertmanager.alertmanager-client.grpc-compression=s2`
+- `-ingester.client.grpc-compression=s2`
+- `-querier.frontend-client.grpc-compression=s2`
+- `-querier.scheduler-client.grpc-compression=s2`
+- `-query-frontend.grpc-client-config.grpc-compression=s2`
+- `-query-scheduler.grpc-client-config.grpc-compression=s2`
+- `-ruler.client.grpc-compression=s2`
+- `-ruler.query-frontend.grpc-client-config.grpc-compression=s2`
+
+Distributors now support `lz4` OTLP compression, and you can deploy them in multiple availability zones.
+
+The ruler's `<prometheus-http-prefix>/api/v1/rules` endpoint now supports the `exclude_alerts`, `group_limit`, and `group_next_token` parameters.
+
+mimirtool's `analyze ruler` and `analyze prometheus` commands now support bearer tokens.
+
+You can now tune HTTP client settings for GCS and Azure backends via an `http` block or corresponding CLI flags.
+
+The compactor now refreshes deletion marks concurrently when updating the bucket index.
+
+You can now set the number of Memcached replicas for each type of cache using configuration settings when using jsonnet.
+
+## Important changes
+
+In Grafana Mimir 2.15, the following behavior has changed:
+
+The following alertmanager metrics are not exported for a `user` label when the metric value is zero:
+
+- `cortex_alertmanager_alerts_received_total`
+- `cortex_alertmanager_alerts_invalid_total`
+- `cortex_alertmanager_partial_state_merges_total`
+- `cortex_alertmanager_partial_state_merges_failed_total`
+- `cortex_alertmanager_state_replication_total`
+- `cortex_alertmanager_state_replication_failed_total`
+- `cortex_alertmanager_alerts`
+- `cortex_alertmanager_silences`
+
+PromQL compatibility has been upgraded from Prometheus 2.0 to 3.0. For more details, refer to the [Prometheus documentation](https://prometheus.io/docs/prometheus/3.0/migration/#promql). The following changes are of note:
+
+- The `.` pattern in regular expressions in PromQL now matches newline characters.
+- Lookback and range selectors are left-open and right-closed. They were previously left-closed and right-closed.
+- Native histograms now use exponential interpolation.
+
+Backwards compatibility in dashboards and alerts for `thanos_memcached_`-prefixed metrics has been removed. These metrics were removed in 2.12 in favor of `thanos_cache_`-prefixed metrics.
+
+Experimental support for Redis as a cache backend has been removed from jsonnet.
+
+The following deprecated configuration options were removed in this release:
+
+- `-distributor.direct-otlp-translation-enabled`, which has been enabled by default since 2.13 and is now considered stable.
+- `-query-scheduler.prioritize-query-components`, which is now always enabled.
+- `-api.get-request-for-ingester-shutdown-enabled`, a deprecated experimental flag which has been marked for removal in 2.15.
+
+## Experimental features
+
+Grafana Mimir 2.15 includes some features that are experimental and disabled by default.
+Use these features with caution and report any issues that you encounter:
+
+You can now enable Mimir's experimental PromQL engine with `-querier.query-engine=mimir`. This new engine provides improved performance and reduced querier resource consumption. However, it only supports a subset of all PromQL features. It falls back to the regular Prometheus engine for queries containing unsupported features.
+
+You can now use the query-frontend to cache non-transient errors using the experimental flags `-query-frontend.cache-errors` and `-query-frontend.results-cache-ttl-for-errors`.
+
+The query-frontend and querier both support an experimental PromQL function, `double_exponential_smoothing`, which you can enable by setting `-querier.promql-experimental-functions-enabled=true` and `-query-frontend.promql-experimental-functions-enabled=true`.
+
+The ingester now supports out-of-order native histogram ingestion via the flag `-ingester.ooo-native-histograms-ingestion-enabled`.
+
+The ingester can now build 24h blocks for out-of-order data which is more than 24 hours old, using the setting `-blocks-storage.tsdb.bigger-out-of-order-blocks-for-old-samples`.
+
+The ruler now supports caching the contents of rule groups via the setting `-ruler-storage.cache.rule-group-enabled`.
+
+The distributor now supports promotion of OTel resource attributes to labels via the setting `-distributor.promote-otel-resource-attributes`.
+
+## Bug fixes
+
+- Alerts: Fix autoscaling metrics joins in `MimirAutoscalerNotActive` when series churn.
+- Alerts: Exclude failed cache "add" operations from alerting since failures are expected in normal operation.
+- Alerts: Exclude read-only replicas from `IngesterInstanceHasNoTenants` alert.
+- Alerts: Use resident set memory for the `EtcdAllocatingTooMuchMemory` alert so that ephemeral file cache memory doesn't cause the alert to misfire.
+- Dashboards: Fix autoscaling metrics joins when series churn.
+- Distributor: Fix pooling buffer reuse logic when `-distributor.max-request-pool-buffer-size` is set.
+- Ingester: Fix issue where active series requests error when encountering a stale posting.
+- Ingester: Fix race condition in per-tenant TSDB creation.
+- Ingester: Fix race condition in exemplar adding.
+- Ingester: Fix race condition in native histogram appending.
+- Ingester: Fix bug in concurrent fetching where a failure to list topics on startup would cause an invalid topic ID (0x00000000000000000000000000000000).
+- Ingester: Fix data loss bug in the experimental ingest storage when a Kafka Fetch is split into multiple requests and some of them return an error.
+- Ingester: Fix bug where chunks could have one unnecessary zero byte at the end.
+- OTLP: Support integer exemplar value type.
+- OTLP receiver: Preserve colons and combine multiple consecutive underscores into one when generating metric names in suffix adding mode (`-distributor.otel-metric-suffixes-enabled`).
+- Prometheus: Fix issue where negation of native histograms (e.g. `-some_native_histogram_series`) did nothing.
+- Prometheus: Always return unknown hint for first sample in non-gauge native histograms chunk to avoid incorrect counter reset hints when merging chunks from different sources.
+- Prometheus: Ensure native histograms counter reset hints are corrected when merging results from different sources.
+- PromQL: Fix issue where functions such as `rate()` over native histograms could return incorrect values if a float stale marker was present in the selected range.
+- PromQL: `round` now removes the metric name again.
+- PromQL: Fix issue where `metric might not be a counter, name does not end in _total/_sum/_count/_bucket` annotation would be emitted even if `rate` or `increase` did not have enough samples to compute a result.
+- Querier: Fix the behavior of binary operators between native histograms and floats.
+- Querier: Fix stddev+stdvar aggregations to always ignore native histograms, and to treat infinity consistently.
+- Query-frontend: Fix issue where sharded queries could return annotations with incorrect or confusing position information.
+- Query-frontend: Fix issue where downstream consumers may not generate correct cache keys for experimental error caching.
+- Query-frontend: Support `X-Read-Consistency-Offsets` on labels queries too.
+- Ruler: Fix issue when using the experimental `-ruler.max-independent-rule-evaluation-concurrency` feature, where the ruler could panic as it updates a running ruleset or shutdowns.
+
+### Helm chart improvements
+
+The Grafana Mimir and Grafana Enterprise Metrics Helm charts are released independently.
+Refer to the [Grafana Mimir Helm chart documentation](/docs/helm-charts/mimir-distributed/latest/).