improve: filter only own updates for read-after-write-consistency

docs/content/en/blog/news/read-after-write-consistency.md

@@ -179,6 +179,11 @@ From this point the idea of the algorithm is very simple:
 2. When the informer propagates an event, check if its resource version is greater than or equal to
    the one in the TRC. If yes, evict the resource from the TRC.
 3. When the controller reads a resource from cache, it checks the TRC first, then falls back to the Informer's cache.
+
+The actual filtering of events for our own writes is more nuanced than a simple
+"evict on RV ≥ TRC version" rule — it is driven by a per-resource state machine
+that tracks in-flight writes and the events received around them. See
+[Filtering events for our own updates](#filtering-events-for-our-own-updates) below.
 
 
 ```mermaid
@@ -221,13 +226,38 @@ sequenceDiagram
 When we update a resource, eventually the informer will propagate an event that would trigger a reconciliation.
 However, this is mostly not desired. Since we already have the up-to-date resource at that point,
 we would like to be notified only if the resource is changed after our change.
-Therefore, in addition to caching the resource, we also filter out events that contain a resource
-version older than or equal to our cached resource version.
-
-Note that the implementation of this is relatively complex, since while performing the update we want to record all the
-events received in the meantime and decide whether to propagate them further once the update request is complete.
 
-However, this way we significantly reduce the number of reconciliations, making the whole process much more efficient.  
+The framework runs a per-resource *event filter window* around each in-flight
+write: it records the resource version returned by our update, buffers any
+related events that arrive in the meantime, and at the end of the window
+decides what (if anything) to surface to the reconciler. The rules:
+
+- **Pure own echo**: if the only events in the window are watch events whose
+  resource versions match our recorded own writes (and the action is `UPDATED`),
+  they are filtered out — the reconciler isn't bothered.
+- **Foreign change in the window**: if a resource version arrived that was *not*
+  one of our own writes — e.g. a third party modified the resource between two
+  of our updates — the framework synthesizes a single `UPDATED` event covering
+  the whole window (`previousResource` = the resource just before the window,
+  `resource` = the latest known state). The reconciler is notified once, with a
+  faithful before/after picture, instead of receiving each underlying watch
+  event individually.
+- **DELETE in the middle**: if the resource was deleted at some point during
+  the window, that DELETE participates in the synthesis. A trailing `DELETED`
+  is surfaced verbatim; a DELETE-then-recreate inside the window collapses to
+  an `UPDATED` from the deleted state to the recreated state.
+- **Held foreign events**: a foreign event that arrives *before* the matching
+  own write echo is buffered until the write completes. This avoids
+  surfacing it as foreign only to immediately overwrite it with a synthesized
+  echo.
+- **ReList**: events arriving while the informer is performing a relist are
+  tagged. Because a relist may have hidden events, the framework defaults to
+  surfacing such events to the reconciler rather than silently filtering
+  them — even when they would otherwise look like our own echoes.
+
+This way we significantly reduce the number of reconciliations, making the whole
+process much more efficient, while preserving the invariant that any
+foreign change reaches the reconciler.
 
 ### The case for instant reschedule
 

docs/content/en/docs/documentation/reconciler.md

@@ -175,6 +175,23 @@ supports stronger guarantees, both for primary and secondary resources. If this
    that resource again. This feature also makes sure that the reconciliation is not triggered from the event from our
    writes.
 
+   The filter is implemented as a per-resource *event filter window* that opens
+   when an update starts and closes when it completes. Inside the window:
+   - Pure own echoes (watch events whose resource version matches one of our
+     recorded own writes) are dropped.
+   - Foreign events received during the window are merged with the surrounding
+     own writes into a single synthesized `UPDATED` event so the reconciler
+     gets a faithful before/after picture rather than each individual watch
+      event. These events are carefully crafted so they correspond to a real-life scenario,
+      and remain fully usable by filters.
+   - A `DELETED` arriving in the window is propagated; a delete-then-recreate
+     inside the window collapses into one synthesized `UPDATED` from the
+     deleted state to the recreated state.
+   - During an informer relist the filter degrades to "surface what we see":
+     events received while a relist is in progress are propagated even when
+     they would otherwise look like own echoes, since the relist may have
+     hidden events.
+
 
 In order to benefit from these stronger guarantees, use [`ResourceOperations`](https://github.com/operator-framework/java-operator-sdk/blob/main/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/api/reconciler/ResourceOperations.java)
 from the context of the reconciliation:   

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/controller/ControllerEventSource.java

@@ -31,8 +31,8 @@
 import io.javaoperatorsdk.operator.processing.event.source.ResourceAction;
 import io.javaoperatorsdk.operator.processing.event.source.filter.OnDeleteFilter;
 import io.javaoperatorsdk.operator.processing.event.source.filter.OnUpdateFilter;
+import io.javaoperatorsdk.operator.processing.event.source.informer.ExtendedResourceEvent;
 import io.javaoperatorsdk.operator.processing.event.source.informer.ManagedInformerEventSource;
-import io.javaoperatorsdk.operator.processing.event.source.informer.TemporaryResourceCache.EventHandling;
 
 import static io.javaoperatorsdk.operator.ReconcilerUtilsInternal.handleKubernetesClientException;
 import static io.javaoperatorsdk.operator.processing.event.source.controller.InternalEventFilters.*;
@@ -141,11 +141,22 @@ private void handleOnAddOrUpdate(
       ResourceAction action, T oldCustomResource, T newCustomResource) {
     var handling =
         temporaryResourceCache.onAddOrUpdateEvent(action, newCustomResource, oldCustomResource);
-    if (handling == EventHandling.NEW) {
-      handleEvent(action, newCustomResource, oldCustomResource, null);
-    } else if (log.isDebugEnabled()) {
-      log.debug("{} event propagation for action: {}", handling, action);
-    }
+    handling.ifPresentOrElse(
+        this::handleEvent,
+        () -> {
+          if (log.isDebugEnabled()) {
+            log.debug("Skipping/deferring event propagation for action: {}", action);
+          }
+        });
+  }
+
+  @SuppressWarnings("unchecked")
+  private void handleEvent(ExtendedResourceEvent r) {
+    handleEvent(
+        r.getAction(),
+        (T) r.getResource().orElseThrow(),
+        (T) r.getPreviousResource().orElse(null),
+        r.isLastStateUnknown());
   }
 
   @Override
@@ -154,10 +165,10 @@ public synchronized void onDelete(T resource, boolean deletedFinalStateUnknown)
         resource,
         ResourceAction.DELETED,
         () -> {
-          temporaryResourceCache.onDeleteEvent(resource, deletedFinalStateUnknown);
+          var res = temporaryResourceCache.onDeleteEvent(resource, deletedFinalStateUnknown);
           // delete event is quite special here, that requires special care, since we clean up
           // caches on delete event.
-          handleEvent(ResourceAction.DELETED, resource, null, deletedFinalStateUnknown);
+          res.ifPresent(this::handleEvent);
         });
   }
 

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/informer/EventFilterSupport.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright Java Operator SDK Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.javaoperatorsdk.operator.processing.event.source.informer;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.javaoperatorsdk.operator.processing.event.ResourceID;
+
+class EventFilterSupport {
+
+  private static final Logger log = LoggerFactory.getLogger(EventFilterSupport.class);
+
+  private final Map<ResourceID, EventFilterWindow> eventFilterWindows = new HashMap<>();
+  private boolean ongoingReList = false;
+
+  public synchronized void startEventFilteringModify(ResourceID resourceID) {
+    var existing = eventFilterWindows.get(resourceID);
+    var ed =
+        eventFilterWindows.computeIfAbsent(resourceID, id -> new EventFilterWindow(ongoingReList));
+    ed.increaseActiveUpdates();
+    log.debug(
+        "startEventFilteringModify: id={}, windowReused={}, ongoingReList={}",
+        resourceID,
+        existing != null,
+        ongoingReList);
+  }
+
+  public synchronized Optional<ExtendedResourceEvent> doneEventFilterModify(ResourceID resourceID) {
+    var ed = eventFilterWindows.get(resourceID);
+    if (ed == null) {
+      log.debug("doneEventFilterModify: no window for id={}", resourceID);
+      return Optional.empty();
+    }
+    ed.decreaseActiveUpdates();
+    log.debug("doneEventFilterModify: id={}", resourceID);
+    return check(ed, resourceID);
+  }
+
+  public synchronized Optional<ExtendedResourceEvent> processEvent(
+      ResourceID resourceId, ExtendedResourceEvent extendedResourceEvent) {
+    var ed = eventFilterWindows.get(resourceId);
+    if (ed != null) {
+      log.debug(
+          "processEvent: buffering event in window. id={}, action={}, rv={}",
+          resourceId,
+          extendedResourceEvent.getAction(),
+          extendedResourceEvent
+              .getResource()
+              .map(r -> r.getMetadata().getResourceVersion())
+              .orElse("?"));
+      ed.addRelatedEvent(extendedResourceEvent);
+      return check(ed, resourceId);
+    } else {
+      log.debug(
+          "processEvent: no active window, surfacing directly. id={}, action={}",
+          resourceId,
+          extendedResourceEvent.getAction());
+      return Optional.of(extendedResourceEvent);
+    }
+  }
+
+  private Optional<ExtendedResourceEvent> check(
+      EventFilterWindow eventFilterWindow, ResourceID resourceID) {
+    var res = eventFilterWindow.check();
+    if (eventFilterWindow.canBeRemoved()) {
+      log.debug("Removing empty event filter window. id={}", resourceID);
+      eventFilterWindows.remove(resourceID);
+    }
+    return res;
+  }
+
+  public synchronized void addToOwnResourceVersions(ResourceID resourceId, String resourceVersion) {
+    var window = eventFilterWindows.get(resourceId);
+    if (window != null) {
+      log.debug("Recording own resourceVersion. id={}, rv={}", resourceId, resourceVersion);
+      window.addToOwnUpdateVersions(resourceVersion);
+    } else {
+      log.debug(
+          "addToOwnResourceVersions: no active window for id={}, rv={} (skipped)",
+          resourceId,
+          resourceVersion);
+    }
+  }
+
+  public synchronized void handleGhostResourceRemoval(ResourceID resourceId) {
+    log.debug("Ghost resource removal: discarding event filter window. id={}", resourceId);
+    eventFilterWindows.remove(resourceId);
+  }
+
+  // for testing purposes
+  synchronized Map<ResourceID, EventFilterWindow> getEventFilterWindows() {
+    return eventFilterWindows;
+  }
+
+  public synchronized void setStartingReList() {
+    log.debug("ReList starting: tagging {} active window(s)", eventFilterWindows.size());
+    ongoingReList = true;
+    eventFilterWindows.values().forEach(EventFilterWindow::setReListStarted);
+  }
+
+  public synchronized void setRelistFinished() {
+    log.debug("ReList finished: clearing tag from {} active window(s)", eventFilterWindows.size());
+    ongoingReList = false;
+    eventFilterWindows.values().forEach(EventFilterWindow::setReListFinished);
+  }
+
+  public synchronized boolean isActiveUpdateFor(ResourceID resourceId) {
+    return eventFilterWindows.containsKey(resourceId);
+  }
+}