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https://issues.apache.org/jira/browse/CURATOR-447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16317058#comment-16317058
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ASF GitHub Bot commented on CURATOR-447:
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Github user dragonsinth commented on the issue:
https://github.com/apache/curator/pull/250
Hi @njhill just got back to work from vacation, and this is a little more
than I can just eyeball, I gotta think through it a bit when I have more time.
I think I would like to see the removal of `nodeState` in isolation, perhaps
with an explicit `PENDING` sentinel rather than just `null`.
It's not clear to me that `TreeNode extends AtomicReference` and `@Nullable
outstandingOps` are wins. The first one doesn't really save any memory, and
for the second one, the ongoing CPU cost to update `outstandingOps` is
basically nothing, it's almost certainly immeasurably tiny, and you have to
introduce racy field reads to accomplish it.
Have you done memory use measurements? I would expect the memory footprint
of `ConcurrentMap<String, TreeNode> children` to mostly dominate the memory
overhead of our own classes, not to mention all the Watchers.
> TreeCache: Improve memory usage and concurrent update logic
> -----------------------------------------------------------
>
> Key: CURATOR-447
> URL: https://issues.apache.org/jira/browse/CURATOR-447
> Project: Apache Curator
> Issue Type: Improvement
> Components: Recipes
> Affects Versions: 3.3.0, 2.12.0
> Reporter: Nick Hill
> Priority: Minor
> Labels: performance
>
> Jira https://issues.apache.org/jira/browse/CURATOR-374 reduced per-node
> memory usage in {{TreeCache}}. It can be improved further via removal of the
> {{nodeState}} field - its {{LIVE}} state corresponds exactly to the adjacent
> {{childData}} field being non-null, and a sentinel {{ChildData}} value can be
> used for the {{DEAD}} state. This simplification also reduces the room for
> bugs and state inconsistencies.
> Other improvements included:
> * A further simplification to have {{TreeNode}} extend {{AtomicReference}},
> which obviates the need for an explicit {{childData}} field
> * More robust cache update logic (in get-children and get-data event
> callbacks)
> * Avoid overhead of incrementing/decrementing the {{outstandingOps}} atomic
> integer post-initialization
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