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From "Peter Schuller (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-3856) consider using persistent data structures for some things
Date Mon, 06 Feb 2012 00:58:00 GMT
consider using persistent data structures for some things
---------------------------------------------------------

                 Key: CASSANDRA-3856
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3856
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Peter Schuller
            Assignee: Peter Schuller
            Priority: Minor


When thinking about CASSANDRA-3831, CASSANDRA-3833, CASSANDRA-3417 (and probably others) I
keep thinking that I really want persistent data structures ala Clojure to enable giving out
stable copies of data without copying, to avoid complicating the code significantly to achieve
a combination of reasonable computational complexity, performance, and thread-safety. However,
I am not about to propose that we introduce Clojure into the code base.

Turns out other people have had similar desires and wanted to see Java varsions of the clojure
data structures (https://github.com/krukow/clj-ds and http://thesoftwarelife.blogspot.com/2009/10/java-immutable-persistent-map.html)
and there is another persistent ds project too (http://code.google.com/p/pcollections/).

The latter in particular looks interesting (not having tested it).

I think it's worth considering adopting the use of these for things like the token meta data.
In general, I'd say it may be worth considering for things that are not performance critical
in the sense of constant factor performance, but where you want thread-safety and reasonable
computational complexity and an easier sense of what's safe from a concurrency perspective.
Currently, we keep having to either copy data to "punt" a concurrency concern, at the cost
of computational complexity, or else add locking at the cost of performance and complexity,
or switch to concurrent data structures at the cost of performance and another type of complexity.

Does this seem completely out of the blue to people or do people agree it's worth exploring?



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