Erik
Hookom, Jacob wrote:
LRU - Least Recently Used. You define your cache size and every time an object is created or "grabbed" from the cache, it gets promoted to the top of the cache, or you can have its timestamp reset to 'now'. As objects are created, you check to see if the cache is too big, if so, take the oldest or the item from the bottom of the stack out of the cache.
Softly Referenced - Instead of putting the actual object as the value in a Hashmap, wrap it in a 'SoftReference' which may loose the object depending on how the garbage collector handles things with memory resources. This allows you to have as much as you want for cached objects, but keep in mind, if the VM needs more memory, your softly-referenced objects are on the chopping block. Depending on the VM to manage your cache can be a little bit more expensive for processing and you will see the GC running a little bit more frequently-- the trade off is that you've maximized your memory usage and with some VM arguments, you can reduce the GC runs into a manageable amount on an enterprise system.
public Object fetchObject(Object identity) { Object result = null; SoftReference ref = this.map.get(identity); if (ref != null) { result = ref.get(); if (result == null) { ref = null; this.map.remove(identity); } } return result; }
-------- Jacob Hookom Senior Programmer/Analyst McKesson Medical Surgical Golden Valley, MN
-----Original Message----- From: Erik Price [mailto:[EMAIL PROTECTED] Sent: Friday, June 20, 2003 3:49 PM To: Struts Users Mailing List Subject: Re: [OT] caching strategy
Hookom, Jacob wrote:
create primary keys for your data, create an identity object to represent legacy data, create a hashmap or cache interface and use either LRU's or Softly referenced caching. Pretty straight forward. Logic would be
"select
primary keys + lastModified" if changed or not found, create, else pull
from
cache.
Okay I understand the first part -- proxy the legacy data entities with Java objects, and use a HashMap-based cache (perhaps using the primary keys as the hash's keys). But...
What are LRU's? Softly referenced caching -- have a particularly good resource on this topic?
Erik
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