Surface avg I/O size (KB) per file in sp_PressureDetector#773
Merged
erikdarlingdata merged 1 commit intodevfrom Apr 29, 2026
Merged
Surface avg I/O size (KB) per file in sp_PressureDetector#773erikdarlingdata merged 1 commit intodevfrom
erikdarlingdata merged 1 commit intodevfrom
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Adds avg_read_kb and avg_write_kb to the file metrics output, computed from sys.dm_io_virtual_file_stats num_of_bytes_read / num_of_reads (and the write counterparts). Values flow through the snapshot temp table, the @log_to_table path, and both the snapshot and delta CTE branches. Helps explain disk-latency findings: a high avg_read_stall_ms paired with a small avg_read_kb says random small reads, while the same stall with a large avg_read_kb says big sequential pulls. Two different remediations.
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Summary
Adds
avg_read_kbandavg_write_kbto the file metrics result set (and the matching@log_to_tablecolumns), computed fromsys.dm_io_virtual_file_stats.num_of_bytes_read / num_of_readsand the write counterparts.A high
avg_read_stall_mswith a smallavg_read_kbpoints at random small reads (index seeks, lookups). The same stall with a largeavg_read_kbpoints at large sequential pulls (read-ahead, scans, restores). Different remediations, same wait — surfacing the size disambiguates.Wired through:
@file_metrics)@log_to_tablepermanent tablefm/f) and delta CTE (fmvsfm2) branchesTest plan
CREATE OR ALTER).EXEC dbo.sp_PressureDetector @minimum_disk_latency_ms = 0, @skip_queries = 1, @skip_waits = 1, @skip_perfmon = 1;— both columns populated with sensible values (e.g. 123.88 KB avg read on a hot data file, 26.69 KB avg write — consistent with 8K page bursts up to 128K read-ahead).@log_to_table = 1to verify the persisted columns land cleanly on a fresh install.