[PR] Optimize single-node CuratorCache storage with AtomicReference [curator]

["waterWang (via GitHub)" <gi...@apache.org>]

waterWang opened a new pull request, #1305:
URL: https://github.com/apache/curator/pull/1305

   ## Summary
   
   When a `CuratorCache` is built with the `SINGLE_NODE_CACHE` option, only one node is ever cached (the root path). Today the cache still uses a `ConcurrentHashMap`-backed `StandardCuratorCacheStorage`, which is overkill and wastes memory for this case. This PR adds a dedicated `SingleNodeCuratorCacheStorage` implementation backed by a single `AtomicReference` and switches the default storage selection to it whenever `SINGLE_NODE_CACHE` is set.
   
   Fixes #1304
   
   ## Changes
   
   - **New `SingleNodeCuratorCacheStorage`** (`curator-recipes/.../cache/SingleNodeCuratorCacheStorage.java`): implements `CuratorCacheStorage` with a single `AtomicReference<ChildData>`. All interface methods (`put`, `remove`, `get`, `size`, `stream`, `clear`) behave identically to `StandardCuratorCacheStorage` for the single-node case:
     - `size()` returns `0` or `1`
     - `stream()` yields at most one element
     - `put`/`get`/`remove` match on the stored node's path, so a single-node cache can never hold entries for multiple paths.
     - Honors the `cacheBytes` flag the same way `StandardCuratorCacheStorage` does.
   - **`CuratorCacheStorage.java`**: adds two factory methods — `singleNode()` and `singleNodeDataNotCached()`.
   - **`CuratorCacheImpl.java`**: the constructor now selects `CuratorCacheStorage.singleNode()` (instead of `standard()`) when `SINGLE_NODE_CACHE` is set and no explicit storage was provided by the caller. Calling `builder(client, path).withStorage(...)` still takes precedence.
   
   ## Behavioral compatibility
   
   - `CuratorCacheStorage` is a public interface and the storage is only switched when the caller did **not** supply a custom storage. Explicit `withStorage()` calls are unchanged.
   - The `SINGLE_NODE_CACHE` option previously only controlled watcher recursion (`recursive = !options.contains(SINGLE_NODE_CACHE)`); this PR additionally optimizes the backing store without changing any observable semantics — `get`, `size`, `stream`, and events all behave the same.
   
   ## Test plan
   
   - Existing `TestCuratorCache` (incl. `testClearOnClose`, `testGreaterThan64kZNodes`) and related cache tests cover the standard path and should remain green.
   - Single-node behavior is exercised by tests that build caches with `SINGLE_NODE_CACHE` and verify `get`/`size`/stream semantics (e.g. `TestCuratorCacheEdges`).


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Re: [PR] Optimize single-node CuratorCache storage with AtomicReference [curator]

["waterWang (via GitHub)" <gi...@apache.org>]

waterWang closed pull request #1305: Optimize single-node CuratorCache storage with AtomicReference
URL: https://github.com/apache/curator/pull/1305


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