release-26.1: server: implement delta profiling for allocs/heap/block/mutex profiles #160804
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Previously, when requesting profiles like allocs, heap, block, or mutex through the pprof UI endpoint (/debug/pprof/ui/allocs/?seconds=10), the seconds parameter was ignored and an immediate snapshot was returned. This differed from the behavior of Go's standard pprof handler at /debug/pprof/allocs?seconds=10, which correctly collected a delta profile over the specified duration. The issue was in profileLocal() which handled these profile types in the default case without respecting req.Seconds. Now, when Seconds > 0 is specified, we collect two profile snapshots separated by the requested duration and compute their difference (delta profile) using the same algorithm as Go's net/http/pprof: scale the first profile by -1 and merge with the second. This enables the pprof UI to show "recent allocations" over a specific time window rather than cumulative allocations since process start. Release note (bug fix): Fixed a bug where the pprof UI endpoints for allocs, heap, block, and mutex profiles ignored the seconds parameter and returned immediate snapshots instead of delta profiles.
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jasonlmfong
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Jan 12, 2026
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Backport 1/1 commits from #160608 on behalf of @tbg.
Previously, when requesting profiles like allocs, heap, block, or mutex through the pprof UI endpoint (/debug/pprof/ui/allocs/?seconds=10), the seconds parameter was ignored and an immediate snapshot was returned. This differed from the behavior of Go's standard pprof handler at /debug/pprof/allocs?seconds=10, which correctly collected a delta profile over the specified duration.
The issue was in profileLocal() which handled these profile types in the default case without respecting req.Seconds. Now, when Seconds > 0 is specified, we collect two profile snapshots separated by the requested duration and compute their difference (delta profile) using the same algorithm as Go's net/http/pprof: scale the first profile by -1 and merge with the second.
This enables the pprof UI to show "recent allocations" over a specific time window rather than cumulative allocations since process start.
Release note (bug fix): Fixed a bug where the pprof UI endpoints for allocs, heap, block, and mutex profiles ignored the seconds parameter and returned immediate snapshots instead of delta profiles.
Epic: none
Release justification: fixes and slightly extends a useful isolated expert debugging observability feature.