PROMETHEUS-3.15.0 release notes and known issues

Summary

[CHANGE] PromQL: A range query whose end was not aligned to step caused subqueries inside it to evaluate past the parent's last actual step, inflating peakSamples in the query stats and against the query.max-samples limit, and wasting storage I/O reading samples that were never used in the result. Add tests to prevent regression of the fix made in #18081 . #18598 [CHANGE] PromQL: Do not register a start timestamp reset if the start timestamp hasn't changed between subsequent samples. #19454 [CHANGE] Logging: Deprecate --log.level ; use runtime.log_level configuration to supply the default level. #19511 [FEATURE] Configuration: Allow changing the process log level through runtime.log_level on configuration reload. #19511 [FEATURE] Prometheus: Add --auto-gomemlimit.refresh-interval flag to periodically re-detect the container or system memory limit and update GOMEMLIMIT at runtime. #18843 [FEATURE] Scraping: Add support for scraping targets via Unix Domain Sockets. #12024 . #18091 [FEATURE] scrape: Implement OM2.0 scrape format. #18606 [ENHANCEMENT] Reduce TSDB head CPU utilization when initializing. #18001 [ENHANCEMENT] Docker SD: Add labels __meta_docker_container_image and __meta_docker_container_image_id . #19386 [ENHANCEMENT] Mixin: Add a p95/p99 remote-write send-batch latency panel to the remote-write dashboard. #19500 [ENHANCEMENT] Mixin: Support native histograms in the remote-write send-batch latency panel. #19522 [ENHANCEMENT] PromQL/TSDB: The --enable-feature=st-storage flag now automatically enables XOR2 float chunk encoding and ST-capable histogram chunk encoding, so you no longer need to pass xor2-encoding and histograms-st-encoding alongside it. #19518 [ENHANCEMENT] Remote write / Alertmanager: upgrade sigv4 to v0.5.0, adding session_name and tags fields for STS AssumeRole sessions. The previously undocumented service_name field is now also documented. #19569 [ENHANCEMENT] Scraping: Support zstd-compressed scrape responses, enabled via feature flag zstd-scrape . #19502 [ENHANCEMENT] TSDB: Stabilize the XOR2 float chunk encoding. --enable-feature=xor2-encoding is deprecated; use storage.tsdb.chunk_encoding.floats: xor2 instead. Check that other software reading the TSDB directly (e.g. Thanos sidecar) supports XOR2 before enabling. #19461 [ENHANCEMENT] TSDB: add prometheus_tsdb_head_appenders_created_total metric. #19411 [ENHANCEMENT] Tracing: add more spans to scrapes, API queries and rule evaluations. #19410 [ENHANCEMENT] UI: Show the effective configuration for each scrape pool on the Targets and Service Discovery pages. #19384 [ENHANCEMENT] scrape: Enable start time synthesis for summary _count and _sum series in scrape appender v2. #19323 [ENHANCEMENT] scrape: stop all pools in parallel for faster shutdowns. #19295 [ENHANCEMENT] storage/remote: Add undocumented failed_request_logging config field to debug log remote write V2 requests on send errors. #19249 [ENHANCEMENT] TSDB: Add fast path for XOR chunk decompression to speed up queries. #18049 [ENHANCEMENT] UI: Improve native histogram table formatting and add a background bar indicating the bucket count. #19332 [ENHANCEMENT] TSDB: Add prometheus_tsdb_head_series_pending_commit_underflow_total to report pending-sample reservation underflows. #19470 [PERF] AWS SD: Build RDS cluster labels once per cluster instead of once per instance. #19504 [PERF] AWS SD: Describe RDS instances of different clusters concurrently, bounded by request_concurrency . #19506 [PERF] AWS SD: Describe each ElastiCache resource once per refresh instead of twice. #19585 [PERF] Remote read: Avoid cloning labels for sampled reads when no external labels are configured. #19503 [PERF] Remote write: Reuse OTLP converter scratch state between requests. #19388 [PERF] scrape: conversion from classic to native histograms should only parse start times when enabled. #19446 [BUGFIX] PromQL: Fix info() enrichment for composite expressions with mixed @ /offset references or selector-free vector branc

Improvements and security content

• [CHANGE] PromQL: A range query whose end was not aligned to step caused subqueries inside it to evaluate past the parent's last actual step, inflating peakSamples in the query stats and against the query.max-samples limit, and wasting storage I/O reading samples that were never used in the result. Add tests to prevent regression of the fix made in #18081 . #18598 [CHANGE] PromQL: Do not register a start timestamp reset if the start timestamp hasn't changed between subsequent samples. #19454 [CHANGE] Logging: Deprecate --log.level ; use runtime.log_level configuration to supply the default level. #19511 [FEATURE] Configuration: Allow changing the process log level through runtime.log_level on configuration reload. #19511 [FEATURE] Prometheus: Add --auto-gomemlimit.refresh-interval flag to periodically re-detect the container or system memory limit and update GOMEMLIMIT at runtime. #18843 [FEATURE] Scraping: Add support for scraping targets via Unix Domain Sockets. #12024 . #18091 [FEATURE] scrape: Implement OM2.0 scrape format. #18606 [ENHANCEMENT] Reduce TSDB head CPU utilization when initializing. #18001 [ENHANCEMENT] Docker SD: Add labels __meta_docker_container_image and __meta_docker_container_image_id . #19386 [ENHANCEMENT] Mixin: Add a p95/p99 remote-write send-batch latency panel to the remote-write dashboard. #19500 [ENHANCEMENT] Mixin: Support native histograms in the remote-write send-batch latency panel. #19522 [ENHANCEMENT] PromQL/TSDB: The --enable-feature=st-storage flag now automatically enables XOR2 float chunk encoding and ST-capable histogram chunk encoding, so you no longer need to pass xor2-encoding and histograms-st-encoding alongside it. #19518 [ENHANCEMENT] Remote write / Alertmanager: upgrade sigv4 to v0.5.0, adding session_name and tags fields for STS AssumeRole sessions. The previously undocumented service_name field is now also documented. #19569 [ENHANCEMENT] Scraping: Support zstd-compressed scrape responses, enabled via feature flag zstd-scrape . #19502 [ENHANCEMENT] TSDB: Stabilize the XOR2 float chunk encoding. --enable-feature=xor2-encoding is deprecated; use storage.tsdb.chunk_encoding.floats: xor2 instead. Check that other software reading the TSDB directly (e.g. Thanos sidecar) supports XOR2 before enabling. #19461 [ENHANCEMENT] TSDB: add prometheus_tsdb_head_appenders_created_total metric. #19411 [ENHANCEMENT] Tracing: add more spans to scrapes, API queries and rule evaluations. #19410 [ENHANCEMENT] UI: Show the effective configuration for each scrape pool on the Targets and Service Discovery pages. #19384 [ENHANCEMENT] scrape: Enable start time synthesis for summary _count and _sum series in scrape appender v2. #19323 [ENHANCEMENT] scrape: stop all pools in parallel for faster shutdowns. #19295 [ENHANCEMENT] storage/remote: Add undocumented failed_request_logging config field to debug log remote write V2 requests on send errors. #19249 [ENHANCEMENT] TSDB: Add fast path for XOR chunk decompression to speed up queries. #18049 [ENHANCEMENT] UI: Improve native histogram table formatting and add a background bar indicating the bucket count. #19332 [ENHANCEMENT] TSDB: Add prometheus_tsdb_head_series_pending_commit_underflow_total to report pending-sample reservation underflows. #19470 [PERF] AWS SD: Build RDS cluster labels once per cluster instead of once per instance. #19504 [PERF] AWS SD: Describe RDS instances of different clusters concurrently, bounded by request_concurrency . #19506 [PERF] AWS SD: Describe each ElastiCache resource once per refresh instead of twice. #19585 [PERF] Remote read: Avoid cloning labels for sampled reads when no external labels are configured. #19503 [PERF] Remote write: Reuse OTLP converter scratch state between requests. #19388 [PERF] scrape: conversion from classic to native histograms should only parse start times when enabled. #19446 [BUGFIX] PromQL: Fix info() enrichment for composite expressions with mixed @ /offset references or selector-free vector branc

Affected products and versions

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