Cache Object

The Cache performance object consists of counters that monitor the file system cache, an area of physical memory that stores recently used data as long as possible to permit access to the data without having to read from the disk. Because applications typically use the cache, the cache is monitored as an indicator of application input/output (I/O) operations. When memory is plentiful, the cache can grow, but when memory is scarce, the cache can become too small to be effective.

Counter Name Description Counter Type
Async Copy Reads/sec Shows the rate at which read operations from pages of the file system cache involve a memory copy of the data from the cache to the application's buffer. The application regains control immediately even if the disk must be accessed to retrieve the page. PERF_COUNTER_COUNTER
Async Data Maps/sec Shows the rate at which an application using a file system, such as NTFS, to map a page of a file into the file system cache, does not wait for the page to be retrieved if it is not in main memory. PERF_COUNTER_COUNTER
Async Fast Reads/sec Shows the rate at which read operations from the file system cache bypass the installed file system and retrieve the data directly from the cache. Normally, file I/O requests invoke the file system to retrieve data from a file, but this path permits data to be retrieved from the cache directly (without file system involvement) if the data is in the cache. Even if the data is not in the cache, one invocation of the file system is avoided. If the data is not in the cache, the request does not wait until the data has been retrieved from the disk, but gets control immediately. PERF_COUNTER_COUNTER
Async MDL Reads/sec Shows the rate at which read operations from the file system cache use a Memory Descriptor List (MDL) to access the pages. The MDL contains the physical address of each page in the transfer, thus permitting Direct Memory Access (DMA) of the pages. If the accessed page(s) are not in main memory, the calling application program does not wait for the pages to be retrieved from disk through a page fault. PERF_COUNTER_COUNTER
Async Pin Reads/sec Shows the rate at which data is read into the file system cache before writing the data back to disk. Pages read in this fashion are pinned in memory at the completion of the read. Pinned pages are those that are read into the file system cache before the system writes data back to the disk at the completion of the read. The file system regains control immediately even if the disk must be accessed to retrieve the page. While pinned, a page's physical address is not altered. PERF_COUNTER_COUNTER
Copy Read Hits % Shows the percentage of cache copy read requests that did not require a disk read to access the page in the cache. A copy read is a file read operation that is satisfied by a memory copy from a page in the cache to the application's buffer. The LAN redirector uses this method for retrieving information from the cache, as does the LAN server for small transfers. This method is also used by the disk file systems. PERF_SAMPLE_FRACTION
Copy Reads/sec Shows the rate at which read operations from pages of the file system cache involve a copy read. PERF_COUNTER_COUNTER
Data Flush Pages/sec Shows the rate at which the file system cache has flushed to disk in response to a request to flush or to satisfy a write-through file write request. More than one page can be transferred on each flush operation. PERF_COUNTER_COUNTER
Data Flushes/sec Shows the rate at which the file system cache has flushed its contents to disk in response to a request to flush or to satisfy a write-through file write request. PERF_COUNTER_COUNTER
Data Map Hits % Shows the percentage of data maps in the file system cache that could be resolved without having to retrieve a page from the disk, because the page was already in physical memory. PERF_SAMPLE_FRACTION
Data Map Pins/sec Shows the rate at which data maps in the file system cache resulted in pinning a page in main memory. PERF_SAMPLE_FRACTION
Data Maps/sec Shows the rate at which a file system, such as NTFS, maps a page of a file into the file system cache to read the page. PERF_COUNTER_COUNTER
Fast Read Not Possibles/sec Shows the rate at which an application program interface (API) function call attempts to bypass the file system to get to data in the file system cache that required invoking the file system. PERF_COUNTER_COUNTER
Fast Read Resource Misses/sec Shows the rate at which cache misses occur because of insufficient resources to satisfy the request. PERF_COUNTER_COUNTER
Fast Reads/sec Shows the rate at which read operations from the file system cache bypass the installed file system and retrieve the data directly from the cache. PERF_COUNTER_COUNTER
Lazy Write Flushes/sec Shows the rate at which the Lazy Writer thread writes to disk. PERF_COUNTER_COUNTER
Lazy Write Pages/sec Shows the rate at which the Lazy Writer thread has written to disk. PERF_COUNTER_COUNTER
MDL Read Hits % Shows the percentage of MDL read requests to the file system cache that did not require disk accesses to provide memory access to the page or pages in the cache. PERF_SAMPLE_FRACTION
MDL Reads/sec Shows the rate at which read operations from the file system cache use an MDL to access the data. The LAN server uses this method for large transfers out of the server. PERF_COUNTER_COUNTER
Pin Read Hits % Shows the percentage of pin read requests that did not require a disk read to provide access to the page in the file system cache. PERF_SAMPLE_FRACTION
Pin Reads/sec Shows the rate at which data is read into the file system cache before writing the data back to disk. Pages read in this fashion are pinned in memory at the completion of the read. PERF_COUNTER_COUNTER
Read Aheads/sec Shows the rate at which read operations from the file system cache detect sequential access to a file. The read aheads permit the data to be transferred in larger blocks than those being requested by the application, reducing the overhead per access. PERF_COUNTER_COUNTER
Sync Copy Reads/sec Shows the rate at which read operations from pages of the file system cache involve a memory copy of the data from the cache to the application's buffer. The file system does not regain control until the copy operation is complete, even if the disk must be accessed to retrieve the page. PERF_COUNTER_COUNTER
Sync Data Maps/sec Shows the rate at which a file system, such as NTFS, maps a page of a file into the file system cache to read the page, and, if it is not in main memory, waits for the page to be retrieved. PERF_COUNTER_COUNTER
Sync Fast Reads/sec Shows the rate which read operations from the file system cache bypass the installed file system and retrieve the data directly from the cache. PERF_COUNTER_COUNTER
Sync MDL Reads/sec Shows the rate at which read operations from the file system cache use an MDL to access the pages. PERF_COUNTER_COUNTER
Sync Pin Reads/sec Shows the rate at which data is read into the file system cache before it is written back to disk. Pages read in this fashion are pinned in memory at the completion of the read. PERF_COUNTER_COUNTER

See also

  • Finding Cache Bottlenecks
  • Finding Memory Bottlenecks
  • Default System Performance Counters

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