imbajin opened a new issue, #3012:
URL: https://github.com/apache/hugegraph/issues/3012
## Summary
While working on #3011, @dpol1 spotted a potential silent-drop bug in the
legacy `EventHub` cache-notification path. This issue tracks the investigation
and fix.
## Root Cause
`Cache.java` defines four string constants:
```java
// present-tense — "command" semantics
String ACTION_INVALID = "invalid";
String ACTION_CLEAR = "clear";
// past-tense — "event happened" semantics
String ACTION_INVALIDED = "invalided";
String ACTION_CLEARED = "cleared";
```
**Producers emit past-tense events:**
| File | Lines | Emitted action |
|------|-------|----------------|
| `CachedGraphTransaction.java` | 400, 414, 428 | `ACTION_INVALIDED`,
`ACTION_CLEARED` |
| `CachedSchemaTransaction.java` | 182, 224, 233, 286 | `ACTION_INVALIDED`,
`ACTION_CLEARED` |
**Local listeners only match present-tense events:**
| File | Lines | Listened action |
|------|-------|----------------|
| `CachedGraphTransaction.java` | 147, 179 | `ACTION_INVALID`,
`ACTION_CLEAR` |
| `CachedSchemaTransaction.java` | 120, 127 | `ACTION_INVALID`,
`ACTION_CLEAR` |
| `CachedSchemaTransactionV2.java` | 117, 137 | `ACTION_INVALID`,
`ACTION_CLEAR` |
## How the Current Bridge Works
`StandardHugeGraph.AbstractCacheNotifier` (`StandardHugeGraph.java:1397`)
listens for `"invalided"`/`"cleared"` and converts them into RPC calls to
remote nodes. Remote nodes then call `AbstractCacheNotifier.invalid/clear()`,
which emits `"invalid"`/`"clear"` on their local hubs — which local listeners
do catch.
```
Local transaction commits
→ notifyChanges("invalided") on local schemaEventHub
→ AbstractCacheNotifier.listener catches "invalided"
→ proxy.invalid(type, id) ← RPC call to remote nodes only
→ Remote node: AbstractCacheNotifier.invalid() emits "invalid" on remote
hub
→ Remote CachedSchemaTransaction.listener catches "invalid" ✓
```
## Where Events Are Silently Dropped
The bridge **only routes to remote nodes via RPC**. The local node never
re-emits `"invalid"` after `"invalided"` is published, which means:
1. **Single-node / no-RPC deployments**: `proxy` is a no-op; `"invalided"`
events from `CachedSchemaTransaction`/`CachedGraphTransaction` are consumed by
`AbstractCacheNotifier` and go nowhere. Local consistency is currently
maintained by direct `updateCache()` calls inside each transaction, but any
secondary consumer that relies solely on the EventHub would miss these events.
2. **If the RPC proxy is misconfigured or unavailable**: The `"invalided"`
event is silently swallowed — no error, no fallback.
3. **Concurrent local transactions**: Due to the `containsListener` guard
(only one listener per hub/event), if a second transaction instance needs to be
notified via EventHub it will not be — a latent hazard in scenarios where
multiple transactions share the same EventHub.
## Suggested Fix
Align the action constants: either
- Have producers emit present-tense (`ACTION_INVALID` / `ACTION_CLEAR`) and
remove the past-tense constants, or
- Have `AbstractCacheNotifier` also re-publish `"invalid"`/`"clear"` locally
after forwarding the RPC, so local listeners are always notified.
The safer approach is option 1: unify on present-tense `ACTION_INVALID` /
`ACTION_CLEAR` throughout, since RaftContext (`RaftContext.java:287,313`)
already uses the present-tense constants correctly.
## Related
- PR #3011 (HStore `CachedSchemaTransactionV2` fix that surfaced this)
- Reported by @dpol1 in
https://github.com/apache/hugegraph/pull/3011#issuecomment-4334740756
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