consider using persistent data structures for some things
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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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