Sun Java System Web Server 7.0 Update 4 Performance Tuning, Sizing, and Scaling Guide

DNS Cache Information

The DNS cache caches IP addresses and DNS names. Web Server uses DNS caching for logging and for access control by IP address. DNS cache is enabled by default. The following example shows DNS cache information as displayed in perfdump:

enabled             yes
CacheEntries        4/1024
HitRatio            62854802/62862912 ( 99.99%)

AsyncDNS Data:
enabled             yes
NameLookups         0
AddrLookups         0
LookupsInProgress   0

The following example shows the DNS Cache information as displayed in the Admin Console:

Table 2–6 DNS Cache Statistics

Total Cache Hits 


Total Cache Misses 


Number of Asynchronous Lookups 

Lookups in Progress 

Asynchronous Lookups Enabled 

Number of Asynchronous Address Lookups Performed 


If the DNS cache is disabled, the rest of this section is not displayed in perfdump. In the Admin Console, the page displays zeros.


By default, the DNS cache is on. You can enable or disable DNS caching in the Admin Console on the configuration's Performance tab ⇒ DNS sub tab, under DNS Cache Settings and selecting or deselecting the DNS Cache Enabled box. To enable or disable it using the command-line-interface, use wadm set-dns-cache-prop and set the enabled property.

Cache Entries (Current Cache Entries / Maximum Cache Entries)

This section in perfdump shows the number of current cache entries and the maximum number of cache entries. In the Admin Console the current cache entries are shown as Total Cache Hits. A single cache entry represents a single IP address or DNS name lookup. The cache should be as large as the maximum number of clients that access your web site concurrently. Note that setting the cache size too high wastes memory and degrades performance.


You can set the maximum size of the DNS cache in the Admin Console in the Maximum Cache Size field on the configuration's Performance tab ⇒ DNS sub tab, under DNS Cache Settings. To set it using the command-line-interface, use wadm set-dns-cache-prop and set the max-entries property. The default cache size is 1024. The value range is 2-32768.

Hit Ratio of Cache Hits and Lookups

The hit ratio in perfdump displays the number of cache hits compared to the number of cache lookups. You can compute this number using the statistics in the Admin Console by dividing the Total Cache Hits by the sum of the Total Cache Hits and the Total Cache Misses.

This setting is not tunable.

Async DNS Enabled/Disabled

Async DNS enabled/disabled displays whether the server uses its own asynchronous DNS resolver instead of the operating system's synchronous resolver. By default, Async DNS is disabled. If it is disabled, this section does not appear in perfdump. To enable it using the Admin Console, on the configuration's Performance tab ⇒ DNS tab, under DNS Lookup Settings, select Asynchronous DNS. To enable it using the command-line interface, use wadm set-dns-prop and set the async property to true.