perf(PromQL): improve performance of FloatHistogram.KahanAdd#18252
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krajorama merged 1 commit intoMar 6, 2026
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Signed-off-by: Linas Medziunas <[email protected]>
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- switching to just allocating the buckets as
[]float64is trivial change - I'm not super familiar with Kahan sum, but skipping the addition if the added value is zero make sense.
Note: I tried Claude on this code, but it ignored our Kahan implementation and just assumed it knew what it was doing and told me it had a bug when adding 0 so this change was a bugfix as well - lol.
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@krajorama thanks for a quick turnaround! Could we also consider landing the benchmark (#18248)? I believe there is still some performance juice to be squeezed out of |
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##### [\`v3.11.0\`](https://github.com/prometheus/prometheus/releases/tag/v3.11.0) - \[CHANGE] Hetzner SD: The `__meta_hetzner_datacenter` label is deprecated for the role `robot` but kept for backward compatibility, use the `__meta_hetzner_robot_datacenter` label instead. For the role `hcloud`, the label is deprecated and will stop working after the 1 July 2026. [#17850](prometheus/prometheus#17850) - \[CHANGE] Hetzner SD: The `__meta_hetzner_hcloud_datacenter_location` and `__meta_hetzner_hcloud_datacenter_location_network_zone` labels are deprecated, use the `__meta_hetzner_hcloud_location` and `__meta_hetzner_hcloud_location_network_zone` labels instead. [#17850](prometheus/prometheus#17850) - \[CHANGE] Promtool: Redirect debug output to stderr to avoid interfering with stdout-based tool output. [#18346](prometheus/prometheus#18346) - \[FEATURE] AWS SD: Add Elasticache Role. [#18099](prometheus/prometheus#18099) - \[FEATURE] AWS SD: Add RDS Role. [#18206](prometheus/prometheus#18206) - \[FEATURE] Azure SD: Add support for Azure Workload Identity authentication method. [#17207](prometheus/prometheus#17207) - \[FEATURE] Discovery: Introduce `prometheus_sd_last_update_timestamp_seconds` metric to track the last time a service discovery update was sent to consumers. [#18194](prometheus/prometheus#18194) - \[FEATURE] Kubernetes SD: Add support for node role selectors for pod roles. [#18006](prometheus/prometheus#18006) - \[FEATURE] Kubernetes SD: Introduce pod-based labels for deployment, cronjob, and job controller names: `__meta_kubernetes_pod_deployment_name`, `__meta_kubernetes_pod_cronjob_name` and `__meta_kubernetes_pod_job_name`, respectively. [#17774](prometheus/prometheus#17774) - \[FEATURE] PromQL: Add `</` and `>/` operators for trimming observations from native histograms. [#17904](prometheus/prometheus#17904) - \[FEATURE] PromQL: Add experimental `histogram_quantiles` variadic function for computing multiple quantiles at once. [#17285](prometheus/prometheus#17285) - \[FEATURE] TSDB: Add `storage.tsdb.retention.percentage` configuration to configure the maximum percent of disk usable for TSDB storage. [#18080](prometheus/prometheus#18080) - \[FEATURE] TSDB: Add an experimental `fast-startup` feature flag that writes a `series_state.json` file to the WAL directory to track active series state across restarts. [#18303](prometheus/prometheus#18303) - \[FEATURE] TSDB: Add an experimental `st-storage` feature flag. When enabled, Prometheus stores ingested start timestamps (ST, previously called Created Timestamp) from scrape or OTLP in the TSDB and Agent WAL, and exposes them via Remote Write 2. [#18062](prometheus/prometheus#18062) - \[FEATURE] TSDB: Add an experimental `xor2-encoding` feature flag for the new TSDB block float sample chunk encoding that is optimized for scraped data and allows encoding start timestamps. [#18062](prometheus/prometheus#18062) - \[ENHANCEMENT] HTTP client: Add AWS `external_id` support for sigv4. [#17916](prometheus/prometheus#17916) - \[ENHANCEMENT] Kubernetes SD: Deduplicate deprecation warning logs from the Kubernetes API to reduce noise. [#17829](prometheus/prometheus#17829) - \[ENHANCEMENT] TSDB: Remove old temporary checkpoints when creating a Checkpoint. [#17598](prometheus/prometheus#17598) - \[ENHANCEMENT] UI: Add autocomplete support for experimental `first_over_time` and `ts_of_first_over_time` PromQL functions. [#18318](prometheus/prometheus#18318) - \[ENHANCEMENT] Vultr SD: Upgrade govultr library from v2 to v3 for continued security patches and maintenance. [#18347](prometheus/prometheus#18347) - \[PERF] PromQL: Improve performance and reduce heap allocations in joins (VectorBinop)/And/Or/Unless. [#17159](prometheus/prometheus#17159) - \[PERF] PromQL: Partially address performance regression in native histogram aggregations due to using `KahanAdd`. [#18252](prometheus/prometheus#18252) - \[PERF] Remote write: Optimize WAL watching used for RW sending to reuse internal buffers. [#18250](prometheus/prometheus#18250) - \[PERF] TSDB: Optimize LabelValues intersection performance for matchers. [#18069](prometheus/prometheus#18069) - \[PERF] UI: Skip restacking on hover in stacked series charts. [#18230](prometheus/prometheus#18230) - \[BUGFIX] AWS SD: Fix EC2 SD ignoring the configured `endpoint` option, a regression from the AWS SDK v2 migration. [#18133](prometheus/prometheus#18133) - \[BUGFIX] AWS SD: Fix panic in EC2 SD when DescribeAvailabilityZones returns nil ZoneName or ZoneId. [#18133](prometheus/prometheus#18133) - \[BUGFIX] Agent: Fix memory leak caused by duplicate SeriesRefs being loaded as active series. [#17538](prometheus/prometheus#17538) - \[BUGFIX] Alerting: Fix alert state incorrectly resetting to pending when the FOR period is increased in the config file. [#18244](prometheus/prometheus#18244) - \[BUGFIX] Azure SD: Fix system-assigned managed identity not working when `client_id` is empty. [#18323](prometheus/prometheus#18323) - \[BUGFIX] Consul SD: Fix filter parameter not being applied to health service endpoint, causing Node and Node.Meta filters to be ignored. [#17349](prometheus/prometheus#17349) - \[BUGFIX] Kubernetes SD: Fix duplicate targets generated by `*DualStack` EndpointSlices policies. [#18192](prometheus/prometheus#18192) - \[BUGFIX] OTLP: Fix ErrTooOldSample being returned as HTTP 500 instead of 400 in PRW v2 histogram write paths, preventing infinite client retry loops. [#18084](prometheus/prometheus#18084) - \[BUGFIX] OTLP: Fix exemplars getting mixed between incorrect parts of a histogram. [#18056](prometheus/prometheus#18056) - \[BUGFIX] PromQL: Do not skip histogram buckets in queries where histogram trimming is used. [#18263](prometheus/prometheus#18263) - \[BUGFIX] Remote write: Fix `prometheus_remote_storage_sent_batch_duration_seconds` measuring before the request was sent. [#18214](prometheus/prometheus#18214) - \[BUGFIX] Rules: Fix alert state restoration when rule labels contain Go template expressions. [#18375](prometheus/prometheus#18375) - \[BUGFIX] Scrape: Fix panic when parsing bare label names without an equal sign in brace-only metric notation. [#18229](prometheus/prometheus#18229) - \[BUGFIX] TSDB: Fail early when `use-uncached-io` feature flag is set on unsupported environments. [#18219](prometheus/prometheus#18219) - \[BUGFIX] TSDB: Fall back to CLI flag values when retention is removed from config file. [#18200](prometheus/prometheus#18200) - \[BUGFIX] TSDB: Fix memory leaks in buffer pools by clearing reference fields before returning buffers to pools. [#17895](prometheus/prometheus#17895) - \[BUGFIX] TSDB: Fix missing mmap of histogram chunks during WAL replay. [#18306](prometheus/prometheus#18306) - \[BUGFIX] TSDB: Fix storage.tsdb.retention.time unit mismatch in file causing retention to be 1e6 times longer than configured. [#18200](prometheus/prometheus#18200) - \[BUGFIX] Tracing: Fix missing traceID in query log when tracing is enabled, previously only spanID was emitted. [#18189](prometheus/prometheus#18189) - \[BUGFIX] UI: Fix tooltip Y-offset drift when using multiple graph panels. [#18228](prometheus/prometheus#18228) - \[BUGFIX] UI: Update retention display in runtime info when config is reloaded. [#18200](prometheus/prometheus#18200)
renovate Bot
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to sdwilsh/ansible-playbooks
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Apr 8, 2026
##### [\`v3.11.0\`](https://github.com/prometheus/prometheus/releases/tag/v3.11.0) - \[CHANGE] Hetzner SD: The `__meta_hetzner_datacenter` label is deprecated for the role `robot` but kept for backward compatibility, use the `__meta_hetzner_robot_datacenter` label instead. For the role `hcloud`, the label is deprecated and will stop working after the 1 July 2026. [#17850](prometheus/prometheus#17850) - \[CHANGE] Hetzner SD: The `__meta_hetzner_hcloud_datacenter_location` and `__meta_hetzner_hcloud_datacenter_location_network_zone` labels are deprecated, use the `__meta_hetzner_hcloud_location` and `__meta_hetzner_hcloud_location_network_zone` labels instead. [#17850](prometheus/prometheus#17850) - \[CHANGE] Promtool: Redirect debug output to stderr to avoid interfering with stdout-based tool output. [#18346](prometheus/prometheus#18346) - \[FEATURE] AWS SD: Add Elasticache Role. [#18099](prometheus/prometheus#18099) - \[FEATURE] AWS SD: Add RDS Role. [#18206](prometheus/prometheus#18206) - \[FEATURE] Azure SD: Add support for Azure Workload Identity authentication method. [#17207](prometheus/prometheus#17207) - \[FEATURE] Discovery: Introduce `prometheus_sd_last_update_timestamp_seconds` metric to track the last time a service discovery update was sent to consumers. [#18194](prometheus/prometheus#18194) - \[FEATURE] Kubernetes SD: Add support for node role selectors for pod roles. [#18006](prometheus/prometheus#18006) - \[FEATURE] Kubernetes SD: Introduce pod-based labels for deployment, cronjob, and job controller names: `__meta_kubernetes_pod_deployment_name`, `__meta_kubernetes_pod_cronjob_name` and `__meta_kubernetes_pod_job_name`, respectively. [#17774](prometheus/prometheus#17774) - \[FEATURE] PromQL: Add `</` and `>/` operators for trimming observations from native histograms. [#17904](prometheus/prometheus#17904) - \[FEATURE] PromQL: Add experimental `histogram_quantiles` variadic function for computing multiple quantiles at once. [#17285](prometheus/prometheus#17285) - \[FEATURE] TSDB: Add `storage.tsdb.retention.percentage` configuration to configure the maximum percent of disk usable for TSDB storage. [#18080](prometheus/prometheus#18080) - \[FEATURE] TSDB: Add an experimental `fast-startup` feature flag that writes a `series_state.json` file to the WAL directory to track active series state across restarts. [#18303](prometheus/prometheus#18303) - \[FEATURE] TSDB: Add an experimental `st-storage` feature flag. When enabled, Prometheus stores ingested start timestamps (ST, previously called Created Timestamp) from scrape or OTLP in the TSDB and Agent WAL, and exposes them via Remote Write 2. [#18062](prometheus/prometheus#18062) - \[FEATURE] TSDB: Add an experimental `xor2-encoding` feature flag for the new TSDB block float sample chunk encoding that is optimized for scraped data and allows encoding start timestamps. [#18062](prometheus/prometheus#18062) - \[ENHANCEMENT] HTTP client: Add AWS `external_id` support for sigv4. [#17916](prometheus/prometheus#17916) - \[ENHANCEMENT] Kubernetes SD: Deduplicate deprecation warning logs from the Kubernetes API to reduce noise. [#17829](prometheus/prometheus#17829) - \[ENHANCEMENT] TSDB: Remove old temporary checkpoints when creating a Checkpoint. [#17598](prometheus/prometheus#17598) - \[ENHANCEMENT] UI: Add autocomplete support for experimental `first_over_time` and `ts_of_first_over_time` PromQL functions. [#18318](prometheus/prometheus#18318) - \[ENHANCEMENT] Vultr SD: Upgrade govultr library from v2 to v3 for continued security patches and maintenance. [#18347](prometheus/prometheus#18347) - \[PERF] PromQL: Improve performance and reduce heap allocations in joins (VectorBinop)/And/Or/Unless. [#17159](prometheus/prometheus#17159) - \[PERF] PromQL: Partially address performance regression in native histogram aggregations due to using `KahanAdd`. [#18252](prometheus/prometheus#18252) - \[PERF] Remote write: Optimize WAL watching used for RW sending to reuse internal buffers. [#18250](prometheus/prometheus#18250) - \[PERF] TSDB: Optimize LabelValues intersection performance for matchers. [#18069](prometheus/prometheus#18069) - \[PERF] UI: Skip restacking on hover in stacked series charts. [#18230](prometheus/prometheus#18230) - \[BUGFIX] AWS SD: Fix EC2 SD ignoring the configured `endpoint` option, a regression from the AWS SDK v2 migration. [#18133](prometheus/prometheus#18133) - \[BUGFIX] AWS SD: Fix panic in EC2 SD when DescribeAvailabilityZones returns nil ZoneName or ZoneId. [#18133](prometheus/prometheus#18133) - \[BUGFIX] Agent: Fix memory leak caused by duplicate SeriesRefs being loaded as active series. [#17538](prometheus/prometheus#17538) - \[BUGFIX] Alerting: Fix alert state incorrectly resetting to pending when the FOR period is increased in the config file. [#18244](prometheus/prometheus#18244) - \[BUGFIX] Azure SD: Fix system-assigned managed identity not working when `client_id` is empty. [#18323](prometheus/prometheus#18323) - \[BUGFIX] Consul SD: Fix filter parameter not being applied to health service endpoint, causing Node and Node.Meta filters to be ignored. [#17349](prometheus/prometheus#17349) - \[BUGFIX] Kubernetes SD: Fix duplicate targets generated by `*DualStack` EndpointSlices policies. [#18192](prometheus/prometheus#18192) - \[BUGFIX] OTLP: Fix ErrTooOldSample being returned as HTTP 500 instead of 400 in PRW v2 histogram write paths, preventing infinite client retry loops. [#18084](prometheus/prometheus#18084) - \[BUGFIX] OTLP: Fix exemplars getting mixed between incorrect parts of a histogram. [#18056](prometheus/prometheus#18056) - \[BUGFIX] PromQL: Do not skip histogram buckets in queries where histogram trimming is used. [#18263](prometheus/prometheus#18263) - \[BUGFIX] Remote write: Fix `prometheus_remote_storage_sent_batch_duration_seconds` measuring before the request was sent. [#18214](prometheus/prometheus#18214) - \[BUGFIX] Rules: Fix alert state restoration when rule labels contain Go template expressions. [#18375](prometheus/prometheus#18375) - \[BUGFIX] Scrape: Fix panic when parsing bare label names without an equal sign in brace-only metric notation. [#18229](prometheus/prometheus#18229) - \[BUGFIX] TSDB: Fail early when `use-uncached-io` feature flag is set on unsupported environments. [#18219](prometheus/prometheus#18219) - \[BUGFIX] TSDB: Fall back to CLI flag values when retention is removed from config file. [#18200](prometheus/prometheus#18200) - \[BUGFIX] TSDB: Fix memory leaks in buffer pools by clearing reference fields before returning buffers to pools. [#17895](prometheus/prometheus#17895) - \[BUGFIX] TSDB: Fix missing mmap of histogram chunks during WAL replay. [#18306](prometheus/prometheus#18306) - \[BUGFIX] TSDB: Fix storage.tsdb.retention.time unit mismatch in file causing retention to be 1e6 times longer than configured. [#18200](prometheus/prometheus#18200) - \[BUGFIX] Tracing: Fix missing traceID in query log when tracing is enabled, previously only spanID was emitted. [#18189](prometheus/prometheus#18189) - \[BUGFIX] UI: Fix tooltip Y-offset drift when using multiple graph panels. [#18228](prometheus/prometheus#18228) - \[BUGFIX] UI: Update retention display in runtime info when config is reloaded. [#18200](prometheus/prometheus#18200)
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Which issue(s) does the PR fix:
Fixes #18249 (partially)
This line allocates a new histogram (with new bucket slices) on every
KahanAddinvocation:prometheus/model/histogram/float_histogram.go
Line 468 in 7cb405b
However, the bucket values in this histogram are initialized to 0:
prometheus/model/histogram/float_histogram.go
Line 2038 in 7cb405b
And they are never set to non-zero values, except (potentially) when reducing the resolution of
otherhistogram:prometheus/model/histogram/float_histogram.go
Lines 495 to 504 in 7cb405b
Therefore, we can avoid allocating
otherChistogram, and only allocateotherCPositiveBucketsand/orotherCNegativeBucketsin caseotherhistogram gets its resolution reduced (which is what this PR does).Benchmark (using #18248) results:
Note that with this change
KahanAddis still ~2 times slower than a plainAdd. I believe this could be optimized more aggressively by only doing a local Kahan compensation inkahanReduceResolutionforotherhistogram. This would allow simplifyingkahanAddBuckets(droppingcompensationBucketsBargument and related code). But, as that might involve some precision tradeoffs, I would leave it for a separate change.Does this PR introduce a user-facing change?