Draft release notes for Mimir 2.9.0

docs/sources/mimir/release-notes/v2.9.md

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+---
+title: "Grafana Mimir version 2.9 release notes"
+menuTitle: "V2.9 release notes"
+description: "Release notes for Grafana Mimir version 2.9"
+weight: 300
+---
+
+# Grafana Mimir version 2.9 release notes
+
+Grafana Labs is excited to announce version 2.9 of Grafana Mimir.
+
+The highlights that follow include the top features, enhancements, and bugfixes in this release. For the complete list of changes, see the [changelog](https://github.com/grafana/mimir/blob/main/CHANGELOG.md).
+
+## Features and enhancements
+
+- **Experimental support for optimized series selection strategy** Reduce the volume of data necessary to complete requests with individual label selectors that are present on a lot of series.
+- **Reduced CPU utilisation for some shuffle sharding scenarios** Mimir queriers will now use significantly less CPU in cases where shuffle sharding is enabled with a high number of shards.
+- **Reduced object storage API calls in compactors and rulers** Mimir 2.9 comes with optimizations that will reduce the amount of times compactors and rulers need to access rules stored in object storage.
+- **Experimental support for streaming chunks from ingester to querier** This is expected to greatly reduce querier memory consumption when evaluating queries that select a large number of series, because chunks streamed from the querier can now be read into memory as needed.
+
+### Helm chart improvements
+
+The Grafana Mimir and Grafana Enterprise Metrics Helm chart is now released independently. See the [Grafana Mimir Helm chart documentation](/docs/helm-charts/mimir-distributed/latest/).
+
+## Important changes
+
+In Grafana Mimir 2.9 we have removed the following previously deprecated or experimental metrics:
+
+- `cortex_bucket_store_chunk_pool_requested_bytes_total`
+- `cortex_bucket_store_chunk_pool_returned_bytes_total`
+
+The following configuration options are deprecated and will be removed in Grafana Mimir 2.11:
+
+- The CLI flag `-querier.query-ingesters-within`. This configuration is moved to per-tenant overrides.
+- The CLI flag `-blocks-storage.bucket-store.bucket-index.enabled`.
+- The CLI flags `-blocks-storage.bucket-store.chunk-pool-min-bucket-size-bytes`, `-blocks-storage.bucket-store.chunk-pool-max-bucket-size-bytes` and `-blocks-storage.bucket-store.max-chunk-pool-bytes`.
+- The CLI flags `querier.iterators` and `-query.batch-iterators`.
+
+The following configuration options that were deprecated in 2.7 are removed:
+
+- The CLI flag `-blocks-storage.bucket-store.chunks-cache.subrange-size`. A fixed value of 16000 is now always used.
+- The CLI flag `-blocks-storage.bucket-store.consistency-delay`.
+- The CLI flag `-compactor.consistency-delay`.
+- The CLI flag `-ingester.ring.readiness-check-ring-health`.
+
+The following experimental options and features are now stable:
+
+- The CLI flag `-query-frontend.query-sharding-max-regexp-size-bytes`.
+- The CLI flag `-query-scheduler.max-used-instances`.
+- The CLI flags `-(alertmanager|blocks|ruler)-storage.storage-prefix`.
+- The CLI flag `-compactor.first-level-compaction-wait-period`.
+- The CLI flags `-usage-stats.enabled` and `-usage-stats.installation-mode`.
+- The CLI flag `-query-frontend.query-sharding-target-series-per-shard`.
+
+The following configuration option defaults were changed:
+
+- The default value for the CLI flag `-query-frontend.query-sharding-max-regexp-size-bytes` was changed from `0` to `4096`. As a result, queries with regex matchers exceeding this limit will not be sharded by default.
+- The default value for the CLI flag `-compactor.partial-block-deletion-delay` was changed from `0s` to `1d`. As a result, partial blocks resulting from a failed block upload or deletion will be cleaned up automatically.
+
+## Bug fixes
+
+- Store-gateway: Detect collisions in the postings cache. [PR 4770](https://github.com/grafana/mimir/pull/4770)
+- Store-gateway: Fix panic caused by cached LabelValues responses with more than 655360 values. [PR 5021](https://github.com/grafana/mimir/pull/5021)