dosubot[bot] commented on issue #2617:
URL:
https://github.com/apache/incubator-hugegraph/issues/2617#issuecomment-2270258314
<!-- Answer -->
The issue you're experiencing with the `cacheEventListener` in
`CachedSchemaTransactionV2` not clearing the local schema cache on other
servers in a multi-server environment is due to the fact that it only listens
to local events and does not propagate cache invalidation events across
different servers. The `cacheEventListener` is registered to listen for cache
events within the same instance, but there is no mechanism to broadcast these
events to other servers in the cluster.
Here's a snippet from the `CachedSchemaTransactionV2` class that illustrates
this:
```java
private void listenChanges() {
// Listen store event: "store.init", "store.clear", ...
Set<String> storeEvents = ImmutableSet.of(Events.STORE_INIT,
Events.STORE_CLEAR,
Events.STORE_TRUNCATE);
this.storeEventListener = event -> {
if (storeEvents.contains(event.name())) {
LOG.debug("Graph {} clear schema cache on event '{}'",
this.graph(), event.name());
this.clearCache(true);
return true;
}
return false;
};
this.store().provider().listen(this.storeEventListener);
// Listen cache event: "cache"(invalid cache item)
this.cacheEventListener = event -> {
LOG.debug("Graph {} received schema cache event: {}",
this.graph(), event);
Object[] args = event.args();
E.checkArgument(args.length > 0 && args[0] instanceof String,
"Expect event action argument");
if (Cache.ACTION_INVALID.equals(args[0])) {
event.checkArgs(String.class, HugeType.class, Id.class);
HugeType type = (HugeType) args[1];
Id id = (Id) args[2];
this.invalidateCache(type, id);
this.resetCachedAll(type);
return true;
} else if (Cache.ACTION_CLEAR.equals(args[0])) {
event.checkArgs(String.class, HugeType.class);
this.clearCache(false);
return true;
}
return false;
};
EventHub schemaEventHub = this.params().schemaEventHub();
if (!schemaEventHub.containsListener(Events.CACHE)) {
schemaEventHub.listen(Events.CACHE, this.cacheEventListener);
}
}
```
The `cacheEventListener` is only listening to events from the local
`EventHub` and does not have a mechanism to communicate with other servers'
`EventHub` instances. Therefore, when a client creates a graph schema on one
server, the cache invalidation event is not propagated to other servers,
resulting in stale cache data on those servers
<sup>[[1]](https://github.com/apache/incubator-hugegraph/blob/master/hugegraph-server/hugegraph-core/src/main/java/org/apache/hugegraph/backend/cache/CachedSchemaTransaction.java)</sup>.
To address this, you would need to implement a distributed event
notification system to propagate events across all instances of the application
running on different servers. This could involve using a message broker or a
distributed event bus to propagate events to all servers in the cluster.
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