patsonluk commented on code in PR #909:
URL: https://github.com/apache/solr/pull/909#discussion_r921636428
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solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java:
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@@ -246,6 +244,95 @@ public boolean canBeRemoved() {
}
}
+ /**
+ * A ConcurrentHashMap of active watcher by collection name
+ *
+ * <p>Each watcher DocCollectionWatch also contains the latest DocCollection
(state) observed
+ */
+ private static class DocCollectionWatches
+ extends ConcurrentHashMap<String,
StatefulCollectionWatch<DocCollectionWatcher>> {
+
+ /**
+ * Gets the DocCollection (state) of the collection which the
corresponding watch last observed
+ *
+ * @param collection the collection name to get DocCollection on
+ * @return The last observed DocCollection(state). if null, that means
there's no such
+ * collection.
+ */
+ private DocCollection getDocCollection(String collection) {
+ StatefulCollectionWatch<DocCollectionWatcher> watch = get(collection);
+ return watch != null ? watch.currentState : null;
+ }
+
+ /**
+ * Gets the active collections (collections that exist) being watched
+ *
+ * @return an immutable set of active collection names
+ */
+ private Set<String> activeCollections() {
+ return this.entrySet().stream()
+ .filter(
+ (Entry<String, StatefulCollectionWatch<DocCollectionWatcher>>
entry) ->
+ entry.getValue().currentState != null)
+ .map(Entry::getKey)
+ .collect(Collectors.toUnmodifiableSet());
+ }
+
+ /**
+ * Updates the latest observed DocCollection (state) of the {@link
StatefulCollectionWatch} if
+ * the collection is being watched
+ *
+ * @param collection the collection name
+ * @param newState the new DocCollection (state) observed
+ * @return whether an active watch exists for such collection
Review Comment:
Thank you for the detailed explanations @HoustonPutman !
So it appears that `constructState` serves at least 2 purposes:
1. Construct the clusterstate again as there are changes in the watched
collection states
2. Notify all the watchers as defined in `changedCollections` param
So i agree that for 1., it only makes sense to re-construct the state if
indeed the doc collection has been changed
As for 2, I don't understand enough to tell whether it matters, like whether
`forciblyRefreshAllClusterStateSlow` would expect all watches be notified,
whether there's any change on the corresponding collection or not. But i trust
your analysis!
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