Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Performance Tuning Guide

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### DNS Cache Information (dns)

The DNS cache caches IP addresses and DNS names. Your server’s DNS cache is disabled by default. In the DNS Statistics for Process ID All page under Monitor in the web-based Administration interface the following statistics are displayed:

#### Enabled

If the DNS cache is disabled, the rest of this section is not displayed.

By default, the DNS cache is off. Enable DNS caching with the Admin Console by setting the DNS value to “Perform DNS lookups on clients accessing the server”.

#### CacheEntries (CurrentCacheEntries / MaxCacheEntries)

The number of current cache entries and the maximum number of cache entries. A single cache entry represents a single IP address or DNS name lookup. Make the cache as large as the maximum number of clients that access your web site concurrently. Note that setting the cache size too high is a waste of memory and degrades performance.

Set the maximum size of the DNS cache by entering or changing the value in the Size of DNS Cache field of the Performance Tuning page.

#### HitRatio

The hit ratio is the number of cache hits divided by the number of cache lookups.

This setting is not tunable.

Note –

If you turn off DNS lookups on your server, host name restrictions will not work and IP addresses will appear instead of host names in log files.

#### Caching DNS Entries

It is possible to also specify whether to cache the DNS entries. If you enable the DNS cache, the server can store hostname information after receiving it. If the server needs information about the client in the future, the information is cached and available without further querying. specify the size of the DNS cache and an expiration time for DNS cache entries. The DNS cache can contain 32 to 32768 entries; the default value is 1024. Values for the time it takes for a cache entry to expire can range from 1 second to 1 year specified in seconds; the default value is 1200 seconds (20 minutes).

#### Limit DNS Lookups to Asynchronous

Do not use DNS lookups in server processes because they are resource-intensive. If you must include DNS lookups, make them asynchronous.

#### Enabled

If asynchronous DNS is disabled, the rest of this section will not be displayed.

#### NameLookups

The number of name lookups (DNS name to IP address) that have been done since the server was started. This setting is not tunable.

#### AddrLookups

The number of address loops (IP address to DNS name) that have been done since the server was started. This setting is not tunable.

#### LookupsInProgress

The current number of lookups in progress.

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