THPDFRangeCacheStatistics Record

Snapshot of source reads, cache hits, prefetch activity, read-ahead depth and admission counters for the coalescing range cache

Declaration

THPDFRangeCacheStatistics= record
  SourceReadCount: Int64;
  SourceBytesRead: Int64;
  CacheHitCount: Int64;
  CacheMissCount: Int64;
  PrefetchRequestCount: Int64;
  PrefetchCompletedCount: Int64;
  PrefetchCancelledCount: Int64;
  SequentialReadCount: Int64;
  RandomReadCount: Int64;
  SuppressedPrefetchCount: Int64;
  CurrentReadAheadBlocks: Integer;
  PeakReadAheadBlocks: Integer;
  DirectTransferCount: Int64;
  DirectTransferBytes: Int64;
  CachedRangeCount: Integer;
  CachedBytes: Int64;
  AdmissionCount: Int64;
  RejectionCount: Int64;
  EvictionCount: Int64;
  FrequencyAdmissionCount: Int64;
  FrequencyRejectionCount: Int64;
  FrequencyAgingCount: Int64;
end;

Unit

HPDFDoc

Fields

Field	Purpose
`SourceReadCount`	Number of reads issued against the underlying source
`SourceBytesRead`	Bytes pulled out of the underlying source
`CacheHitCount`	Read requests served wholly out of cached ranges
`CacheMissCount`	Read requests that had to go to the source
`PrefetchRequestCount`	Background prefetch ranges that were requested
`PrefetchCompletedCount`	Background prefetch ranges that ran to completion
`PrefetchCancelledCount`	Background prefetch ranges cancelled, usually by foreground demand
`SequentialReadCount`	Reads classed as sequential by the access pattern detector
`RandomReadCount`	Reads classed as random
`SuppressedPrefetchCount`	Prefetch attempts held back by the admission heuristics
`CurrentReadAheadBlocks`	Read-ahead depth the adaptive controller is using at present
`PeakReadAheadBlocks`	Highest read-ahead depth that was reached
`DirectTransferCount`	Transfers that bypassed the cache altogether
`DirectTransferBytes`	Bytes moved across by bypass transfers
`CachedRangeCount`	Cache entries resident at present
`CachedBytes`	Bytes held by cache entries at present
`AdmissionCount`	Ranges that were admitted into the cache
`RejectionCount`	Ranges that were refused admission on size or policy grounds
`EvictionCount`	Cache entries evicted so as to respect byte and entry budgets
`FrequencyAdmissionCount`	Admissions the frequency sketch credited as reused blocks
`FrequencyRejectionCount`	Admissions refused because the frequency sketch saw no sign of reuse
`FrequencyAgingCount`	Ageing operations performed on the frequency sketch

Usage notes

Read it with the cache source's GetStatistics method; the snapshot is taken under the cache lock, so it is internally consistent
A high SuppressedPrefetchCount together with a low hit rate points to random access where prefetching does not pay off
CachedRangeCount, CachedBytes and FrequencyAgingCount are sampled live from the cache rather than accumulated

THPDFRangeCacheStatistics Record

Declaration

Unit

Fields

Usage notes

Related APIs