windows_exporter/internal/collector/pagefile/AGENTS.md

pagefile collector

The collector reads the multi-instance PDH object Paging File with pdh.CounterTypeRaw. The object exists on every Windows host with a page file, so no role is needed. It also uses GetPerformanceInfo for the page size and os.Stat for the file size. These notes were recorded on Windows Server 2025 (build 26100) with one page file.

• Instances are the page file paths, here C:\pagefile.sys, plus _Total. _Total is dropped because the collector does not request it. The instance name had no \??\ prefix on this host. The file label is the instance name with any \??\ prefix removed.
• % Usage and % Usage Peak are PERF_RAW_FRACTION. Despite the %, the raw value is the number of pages in use (a gauge) and the base (,secondvalue) is the page file size in pages. With 4096-byte pages, the base 622592 matched the file size of 2550136832 bytes from os.Stat and the 2432 MB AllocatedBaseSize of Win32_PageFileUsage.
• % Usage was 128462 pages in the dump and 0 in a later live sample.

Counter reference

Recorded on Windows Server 2025 (build 26100). Raw and Base are the first and second values that pdh.CounterTypeRaw returns for the sample instance.

Paging File

Multi-instance. Instances: _Total, C:\pagefile.sys. Sample instance: C:\pagefile.sys.

Counters the collector reads:

Counter	Type	Raw	Base
% Usage	PERF_RAW_FRACTION	128462	622592

Not read by the collector:

• PERF_RAW_FRACTION: % Usage Peak