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From <>
Subject re: Event order lost with PathChildrenCache
Date Wed, 02 Jul 2014 08:05:05 GMT

I have been experiencing some intermittent issues around ordering on the lines of
and I wondered if someone could confirm/deny a narrow guarantee.

Ideally I’d like to see all operations through the PCC in the order that they happen in
Zookeeper, ie ordered by zxid.

That doesn’t happen around startup, and there is certainly potential for races around the
synchronous operations in my initial:

    readCache.start(PathChildrenCache.StartMode.BUILD_INITIAL_CACHE); // Start eagerly.

and the subsequent operations that keep that cache up to date.  I do see occasional upsets

But I have a more practical question.

Once all the initial/startup work is over and the cache is in a steady state, if node A is
updated and then node B in Zookeeper, is a user of the PCC guaranteed NOT to see an update
on B before an update of A?

Why? So I can do a bunch of node updates then update a 'beacon' node B, which can trigger
(re-)reading of all other/earlier nodes knowing them now to be in the latest state in all
PCC caches.



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