File Cache Statistics Information

The cache information section provides statistics on how your file cache is being used. The file cache is an in-memory cache that stores frequently accessed objects from the proxy server's disk cache.

For performance reasons, Proxy Server caches as follows:

• For small files, it caches the content in memory (heap).

• For medium files, it caches the content using mmap.

• For large files, it caches the open file descriptors to avoid opening and closing files.

The following is an example of how the cache statistics are displayed in perfdump:

CacheInfo:
------------------
File Cache Enabled       yes
File Cache Entries       141/1024
File Cache Hit Ratio     652/664 ( 98.19%)
Maximum Age              30
Accelerator Entries      120/1024
Acceleratable Requests   281/328 ( 85.67%)
Acceleratable Responses  131/144 ( 90.97%)
Accelerator Hit Ratio    247/281 ( 87.90%)

The following table shows the file cache statistics as displayed in the Admin Console:

Accelerator Entries

The number of files that have been cached in the accelerator cache.

Tuning

You can increase the maximum number of accelerator cache entries by increasing the number of file cache entries as described in File Cache Entries. Note that this number will typically be smaller than the File Cache Entries number because the accelerator cache only caches information about files and not directories. If the number is significantly lower than the File Cache Entries number, you can improve the accelerator cache utilization by following the tuning information described in Acceleratable Requests and Acceleratable Responses.

Acceleratable Requests

The number of client requests that were eligible for processing by the accelerator cache. Only simple GET requests are processed by the accelerator cache. The accelerator cache does not process requests that explicitly disable caching, for example, requests sent when a user clicks Reload in the browser.

Tuning

To maximize the number of acceleratable requests, structure your web sites to use static files when possible and avoid using query strings in requests for static files.

Acceleratable Responses

The number of times the response to an acceleratable request was eligible for addition to the accelerator cache.

Accelerator Hit Ratio

The number of times the response for a request that can be accelerated was found in the accelerator cache.

Tuning

Higher hit ratios result in better performance. To maximize the hit ratio, see the tuning information for Acceleratable Responses.

File Cache Enabled

If the cache is disabled, the rest of this section is not displayed in perdump. In the Admin console, the File Cache Statistics section shows zeros for the values.

Tuning

The cache is enabled by default. You can disable it in the Admin console at "Configure File Cache" sub-tab in the "Caching" tab.

File Cache Entries

The number of current cache entries and the maximum number of cache entries are both displayed in perfdump. In the Admin console, they are called the Number of Entries and the Maximum Cache Size. A single cache entry represents a single URI.

Tuning

The available address space for a 32-bit process like the Proxy server is limited to 4Gbytes. The max-entries for file cache is based on the number of threads (as specified by thread-pool/max-threads), and the connection queue size. It is recommended to cache small, frequently accessed cache files in the file cache and use perfdump to ensure that the file cache hit ratio is close to 100%. To achieve this, you may increase file cache size and fine tune the max-entries for optimal performance.

File Cache Hit Ratio

The hit ratio available through perfdump gives you the number of file cache hits compared to cache lookups. Numbers approaching 100% indicate that the file cache is operating effectively, while numbers approaching 0% indicate that the file cache is not serving many requests.

To figure this number yourself using the statistics provided through the Admin console, divide the Total Cache Hits by the sum of the Total Cache Hits and the Total Cache Misses.

This setting is not tunable.

Maximum Age

This field displays the maximum age of a valid cache entry. The parameter controls how long cached information is used after a file has been cached. An entry older than the maximum age is replaced by a new entry for the same file.

Maximum Heap Cache Size

The optimal cache heap size depends upon how much system memory is free. A larger heap size means that the Proxy Server can cache more content and therefore obtain a better hit ratio. However, the heap size should not be so large that the operating system starts paging cached files.

File Cache Dynamic Control and Monitoring

File Cache stores file contents in the memory. You can add an object to obj.conf to dynamically monitor and control the file cache while the server is running.

To Control and Monitor the File Cache

1. Add a NameTrans directive to the default object:

   NameTrans fn="assign-name" from="/nsfc" name="nsfc"

2. Add an nsfc object definition:

   <Object name="nsfc">
   Service fn="service-nsfc-dump"
   </Object>

   This configuration enables the file cache control and monitoring function (nsfc-dump) to be accessed through the URI /nfsc. To use a different URI, change the from parameter in the NameTrans directive.

   The following is an example of the information you receive when you access the URI:

   Sun Java System File Cache Status (pid 3602) The file cache is enabled. Cache resource utilization Number of cached file entries = 174968 (152 bytes each, 26595136 total bytes) Heap space used for cache = 1882632616/1882632760 bytes Mapped memory used for medium file contents = 0/1 bytes Number of cache lookup hits = 47615653/48089040 ( 99.02 %) Number of hits/misses on cached file info = 23720344/324195 Number of hits/misses on cached file content = 16247503/174985 Number of outdated cache entries deleted = 0 Number of cache entry replacements = 0 Total number of cache entries deleted = 0 Parameter settings ReplaceFiles: false ReplaceInterval: 1 milliseconds HitOrder: false CacheFileContent: true TransmitFile: false MaxAge: 3600 seconds MaxFiles: 600000 files SmallFileSizeLimit: 500000 bytes MediumFileSizeLimit: 1000001 bytes BufferSize: 8192 bytes CopyFiles: false Directory for temporary files: /tmp Hash table size: 1200007 buckets

   You can include a query string when you access the URI. The following values are recognized:

   • ?list: Lists the files in the cache.

   • ?refresh=n: Causes the client to reload the page every n seconds.

   • ?restart: Causes the cache to be shut down and then restarted.

   • ?start: Starts the cache.

   • ?stop: Shuts down the cache.

   If you choose the ?list option, the file listing includes the file name, a set of flags, the current number of references to the cache entry, the size of the file, and an internal file ID value. The flags are as follows:

   • C: File contents are cached.

   • D: Cache entry is marked for delete.

   • E: PR_GetFileInfo() returned an error for this file.

   • I: File information including size and modification date is cached.

   • M: File contents are mapped into virtual memory.

   • O: File descriptor is cached (when TransmitFile is set to true).

   • P: File has associated private data and appears on shtml files.

   • T: Cache entry has a temporary file.

   • W: Cache entry is locked for write access.