Re: Best database for implementing a cache

From:
=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 31 Mar 2007 19:53:21 -0400
Message-ID:
<460ef467$0$90276$14726298@news.sunsite.dk>
vj wrote:

Certainly thats a good idea. How aboute mainting a hashtable and a
priority queue. The hashtable will store all the meta data associated
with a file and the priority queue will implement file aviction
policy. as soon as a a file is hit i will increase the hit count. On a
cache miss i will fetch the image , create an entry in the hash table
and push an entry in the queue. if the queue size if creater than a
certain treshhold i will pop the element from its head (with the
lowest access count) delete its corrosponding file / hashtable entry.

This seems to be a good idea but i have a small doubt. Does propirity
queue dynamicaly orders elements. I mean since the priority queue is
implemented as a heap in java hence element ordring only takes place
when elements are added. This will create problems as because if i
update access count in hashtable then they wont be reflected in the
structure of the queue. Hence when i pop element from its head for
eviction it might not be the one with minimum access count.

What do you think, Any other data structure that we can use for fast
lookup of elements


What about:
HastMape, key=filename, value=(file content, list with access times)
cleanup code triggered either by time or every n'th access iterates over
HashMap and:
   - remove entries that have too few or too old accesses
   - trim list with access times for too old accesses for entries kept
?

Arne

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