Monitoring and Tuning Your Server
Monitoring and Tuning Your Server |
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As Table 5.2 shows, cache performance is judged by how often objects sought in the cache are found. Frequent cache misses result in disk I/O and decreased performance. There are no fixed standards for cache performance, although a value of 80 to 90 percent for Cache Hits % is considered to be excellent for sites with many static files. If Cache Hits and Cache Hits % are very low, or if Cache Misses is quite high, the cache could be too small to function effectively. Adding memory increases the size of the cache and should improve its performance.
Cache flushes can also affect the performance of the IIS Object Cache. Cache flushes are regulated, in part, by an internal timer. The timer activates the object-cache scavenger, which deletes expired objects. Objects are flushed from the cache if they change, or if they time out before they are reused.
To measure cache flushes, compare the number of cache flushes over time to the number of cache misses and to the rate of page faults in the Inetinfo process (as indicated by the Process\ Page Faults/sec: Inetinfo counter). It is important to observe these values over time. Like the other global IIS 5.0 counters, Cache Flushes displays an instantaneous value, not an average. If a high rate of cache flushes is associated with elevated cache misses and page faults, it is possible that the cache is being flushed too frequently.
If you suspect that cache flushes are occurring too often or not often enough, you can change the rate at which unreferenced objects are flushed from the IIS Object Cache. Make sure your server has ample memory before you increase the time between flushes. The cache flush time defaults to 30 seconds; to change it, add the ObjectCacheTTL key to the registry if it is not already present. Put this key in the following registry location:
HKEY_LOCAL_MACHINE
\System
\CurrentControlSet
\Services
\Inetinfo
\Parameters
Caution Do not use a registry editor to edit the registry directly unless you have no alternative. The registry editors bypass the standard safeguards provided by administrative tools. These safeguards prevent you from entering conflicting settings or settings that are likely to degrade performance or damage your system. Editing the registry directly can have serious, unexpected consequences that can prevent the system from starting and require that you reinstall Windows 2000. To configure or customize Windows 2000, use the programs in Control Panel or Microsoft® Management Console (MMC) whenever possible.
If you increase ObjectCacheTTL, the cache size increases because files stay in the cache longer. Be sure your server has enough physical memory to support the increased load.