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Zookeeper, mail # dev - DataTree as HashMap and tree?


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DataTree as HashMap and tree?
Thomas Koch 2010-12-03, 20:05
Hi,

the DataTree structure on the ZK server stores each DataNode in a
ConcurrentHashMap (DataTree.nodes) and in a a double-linked tree of DataNodes.
The class' javadoc says that the additional hashmap is used for fast lookup.

Have you ever done a benchmark, whether the hashmap really provides a
significant speed improvement compared to traversing the tree?

Example: I want to lookup the DataNode /a/b/c. Traversing the tree means I
have to make three lookups in children lists of nodes. The current code makes
one lookup in the big hashmap of _all_ nodes. I doubt, that the current code
is really faster, but I wanted to ask here before programming a benchmark.

Together with this question goes another one: I have some ideas about
improving Path handling, which could significantly save memory but could make
path operations more CPU intensive by one magnitude. In your experience with
large ZK installations, is CPU an issue? Is memory such an issue that you
would trade some CPU for it?

Best regards,

Thomas Koch, http://www.koch.ro