Fix #1048: stop reporting 100% host CPU on SQL Server on Linux#1049
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On SQL Server on Linux the SCHEDULER_MONITOR ring buffer reports SystemIdle = 0 (a documented platform limitation — Microsoft's own sample query carries the comment "SystemIdle on Linux will be 0"). The CPU collector derives other_process_cpu_utilization as 100 - SystemIdle - ProcessUtilization, so on Linux that becomes 100 - 0 - sqlcpu and the host total (sqlserver + other) pins at 100% forever. SQL Server's own CPU number is correct; only the host/other figure is fabricated, and no DMV exposes true host CPU on Linux. Fix: detect Linux (sys.dm_os_host_info.host_platform, via sp_executesql so SQL 2016 never binds the 2017+ DMV) and store NULL for other_process_cpu_utilization on Linux instead of a false value. Every consumer then degrades to the correct SQL-only figure: - install/18 + Lite RemoteCollectorService.Cpu: store NULL on Linux. - install/02: other_process_cpu_utilization made nullable; NULL propagates to the total_cpu_utilization computed column. - upgrades/2.11.0-to-2.12.0/03: migrate existing tables — drop the persisted computed column, widen the base column to NULL, re-add the computed column (ALTER COLUMN is blocked while the computed column depends on it). Idempotent and partial-failure safe. - install/47 views + Dashboard ResourceMetrics/Overview reads: coalesce total to ISNULL(total, sqlserver) so charts, MCP, and high-CPU detection fall back to SQL CPU rather than NULL/0/100 on Linux. Windows behavior is unchanged (host_platform != Linux). Fact collectors, anomaly/baseline/drilldown, and FinOps already key on sqlserver_cpu_utilization or coalesce NULLs to 0, so they degrade consistently. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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… on Linux The erikdarlingdata#1049 fix corrected every path that reads CPU from the collected table (collector, views, chart reads), but the alert engine doesn't read that table — DatabaseService.NocHealth.GetCpuPercentAsync runs its own live query against sys.dm_os_ring_buffers and was never touched. It computes other_cpu_percent = 100 - SystemIdle - ProcessUtilization, and since SystemIdle is always 0 on SQL Server on Linux, that returns 100 - sqlcpu. AlertHealthResult.TotalCpuPercent then sums to a permanent 100%, so AlertStateService's TotalCpuPercent >= CpuThresholdPercent check fires the host-CPU alert forever — exactly what the reporter still saw after installing the nightly. Fix: apply the same Linux guard used by install/18, RemoteCollectorService.Cpu, and FinOps.Inventory — detect host_platform via sp_executesql behind an OBJECT_ID(N'sys.dm_os_host_info', N'V') check (so SQL 2016 never binds the 2017+ DMV) and return NULL for other_cpu_percent on Linux. The existing TotalCpuPercent getter already falls back to the SQL-only figure when OtherCpuPercent is null, so the alert clears. Windows behavior is unchanged. Dashboard-only change — no schema or installer impact. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Problem
Reported in #1048: on SQL Server 2019 on Linux, the Dashboard's host CPU reads 100% constantly while the host is barely busy. SQL Server's own CPU number is correct — only the host/other-process figure is wrong.
Root cause (web-confirmed)
The CPU collector reads
RING_BUFFER_SCHEDULER_MONITORand derivesother_process = 100 - SystemIdle - ProcessUtilization. On Linux,SystemIdleis always0— a documented platform limitation. Microsoft's own sample query carries the literal comment-- SystemIdle on Linux will be 0. Soother = 100 - 0 - sqlcpu, host total =100 - SystemIdle= 100% forever. No DMV exposes true host CPU on Linux.Fix
Detect Linux (
sys.dm_os_host_info.host_platform, viasp_executesqlso SQL 2016 never binds the 2017+ DMV) and storeNULLforother_process_cpu_utilizationon Linux instead of fabricating it. Every consumer degrades to the correct SQL-only figure.install/18_collect_cpu_utilization_stats.sqlNULLfor other-process on LinuxLite/Services/RemoteCollectorService.Cpu.csNULLto DuckDBinstall/02_create_tables.sqlother_process_cpu_utilization→ nullable (fresh installs);NULLpropagates to thetotal_cpu_utilizationcomputed columnupgrades/2.11.0-to-2.12.0/03_make_other_process_cpu_nullable.sqlinstall/47_create_reporting_views.sqlcpu_spikes+daily_summarycoalescetotal → ISNULL(total, sqlserver)so high-CPU is still detected via SQL CPU on LinuxDashboard/Services/DatabaseService.ResourceMetrics.cs,…/Overview.csISNULLcoalesce in the chart query, MCP query, and daily-summary predicateAll other CPU consumers (fact collectors, anomaly/baseline/drilldown, FinOps) already key on
sqlserver_cpu_utilizationor coalesce NULLs to 0, so they degrade consistently. The installer re-runsinstall/*on upgrade, so the collector/view edits reach existing installs automatically.Testing
Validated on sql2022 (live):
NULLother-process propagates toNULLtotal through the computed column0on Windows → Windows behavior unchangedNot tested: the actual Linux
NULLpath — all available SQL instances (2016–2025) are Windows and the behavior can't be faked without the Linux DMV. The logic (host_platform = 'Linux'→ NULL) is straightforward; a real Linux instance is the only true confirmation.Scope note: uses
NULL+ SQL-only fallback rather than an explicit "host CPU N/A on Linux" chart badge (WPF work, not visually verifiable in this environment). On Linux the Dashboard CPU chart's "Total" line sits on top of the "SQL" line.🤖 Generated with Claude Code