Managing the cache size and cache storage

Resolver cache information is maintained in 64-bit private storage in the resolver address space, which is also referred to as the storage above the 2 GB bar. This means that caching does not impact common storage.

The default maximum size of the cache is 200 megabytes. The size is allocated incrementally, as the cache increases. For planning purposes, assume that 1 megabyte of storage holds between 400 and 450 cache entries. The actual number of cache entries depends on the amount of storage used for cache infrastructure control blocks, which varies depending on the number of name servers and the number of entries. If you want to control the maximum size of the cache instead of using the 200 megabyte default, you can use the CACHESIZE resolver setup statement. The CACHESIZE statement specifies the maximum amount of storage, in megabytes, that can be allocated by the resolver to manage cached records. The CACHESIZE statement is also used to determine the upper limit of storage that can be used for negative cache entries. If you use the default CACHESIZE value of 200M, then no more than 40 megabytes of that storage will be used for negative cache entries.

The resolver does not automatically delete expired records (those records whose TTL value has been exceeded). Regardless of the amount of cache storage that is in use, the resolver deletes expired records if a new request is received for the expired resource. The resolver also deletes expired records when your cache storage usage has reached the following levels, and takes additional actions to reduce your storage usage.

• When cache storage is less than 75 percent full, the resolver deletes all expired records approximately every 10 minutes, without waiting for a new request to be processed.
• When cache storage is 75 - 97 percent full, the resolver deletes all expired records approximately every minute, without waiting for a new request to be processed.
• When cache storage is 98 percent or more full, the resolver deletes all expired records approximately every 30 seconds, without waiting for a new request to be processed. The resolver does not add new records to the cache while usage is greater than 99 percent. Message EZZ9307E is displayed until usage is less than 90 percent, you increase the CACHESIZE value, or you delete the contents of the cache; see Step for deleting cache entries for more information.