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Jan-Otto KröpkeandClaude
89c5df9d8b
Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Claude <noreply@anthropic.com>
28 lines
1.7 KiB
Markdown
28 lines
1.7 KiB
Markdown
# iis collector
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- The `Web Service` and `Web Service Cache` objects are served by the perflib
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V1 provider `w3ctrs.dll`, which reads a counter snapshot that W3SVC writes to
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shared memory. When the snapshot is older than `FreshTimeForCounters`
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(default 15 s), the provider signals W3SVC, calls `Sleep` for
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`CheckCountersEveryNMiliseconds` (default 250 ms) and checks the snapshot
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again, up to `NumberOfTimesToCheckCounters` (default 4) times. The defaults
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are built into the DLL; nonzero `REG_DWORD` values below
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`HKLM\SYSTEM\CurrentControlSet\Services\W3SVC\Performance` override them.
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Microsoft does not document these values.
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- So a scrape that hits a stale snapshot waits 250 ms, up to 4 × 250 ms,
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inside `PdhCollectQueryData` of the `Web Service` query. Go execution traces
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from a production server showed 259 to 261 ms there, and PDH reads of
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`system`, `logical_disk` and `net` that started at the same moment blocked
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for the same time. `cpu`, `memory` and the other IIS objects, including
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`Web Service Cache`, were never slow, and there were no IIS event log
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entries. The exact lock inside Windows that makes the other reads wait is
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not known
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([#2698](https://github.com/prometheus-community/windows_exporter/issues/2698)).
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- This is Windows behavior, not an exporter lock or timeout. Don't look for an
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exporter-side cause of flat ~250 ms `iis` durations, and don't add
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workarounds that hide them. A repro on a GitHub runner with IIS did not show
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it in 40 minutes, so don't expect to reproduce it in CI.
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- To find which Windows call a collector blocks in, capture a Go execution
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trace with `--debug.enabled` and `/debug/pprof/trace?seconds=600`. Collectors
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waiting in a Windows call use no CPU, so a CPU profile does not show it.
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