rpuch commented on code in PR #4684:
URL: https://github.com/apache/ignite-3/pull/4684#discussion_r1833803412


##########
modules/replicator/src/main/java/org/apache/ignite/internal/replicator/ReplicaManager.java:
##########
@@ -1086,16 +1097,64 @@ private void idleSafeTimeSync() {
         }
     }
 
-    private void sendSafeTimeSyncIfReplicaReady(CompletableFuture<Replica> 
replicaFuture) {
-        if (isCompletedSuccessfully(replicaFuture)) {
-            Replica replica = replicaFuture.join();
+    private void sendSafeTimeSyncIfReplicaReady(CompletableFuture<Replica> 
replicaFuture, HybridTimestamp proposedSafeTime) {
+        if (!isCompletedSuccessfully(replicaFuture)) {
+            return;
+        }
 
-            ReplicaSafeTimeSyncRequest req = 
REPLICA_MESSAGES_FACTORY.replicaSafeTimeSyncRequest()
-                    .groupId(toReplicationGroupIdMessage(replica.groupId()))
-                    .build();
+        Replica replica = replicaFuture.join();
 
-            replica.processRequest(req, localNodeId);
+        if (!shouldAdvanceIdleSafeTime(replica, proposedSafeTime)) {
+            // If previous attempt might still be waiting on the Metastorage 
SafeTime, we should not send the command ourselves as this
+            // might be an indicator that Metastorage SafeTime has stuck for 
some time; if we send the command, it will have to add its
+            // future, increasing (most probably, uselessly) heap pressure.
+            return;
         }
+
+        getOrCreateContext(replica).lastIdleSafeTimeProposal = 
proposedSafeTime;
+
+        ReplicaSafeTimeSyncRequest req = 
REPLICA_MESSAGES_FACTORY.replicaSafeTimeSyncRequest()
+                .groupId(toReplicationGroupIdMessage(replica.groupId()))
+                .proposedSafeTime(proposedSafeTime)
+                .build();
+
+        replica.processRequest(req, localNodeId).whenComplete((res, ex) -> {
+            if (ex != null) {
+                LOG.error("Could not advance safe time for {} to {}", 
replica.groupId(), proposedSafeTime);
+            }
+        });
+    }
+
+    private boolean shouldAdvanceIdleSafeTime(Replica replica, HybridTimestamp 
proposedSafeTime) {
+        if (placementDriver.getCurrentPrimaryReplica(replica.groupId(), 
proposedSafeTime) != null) {
+            // We know a primary is guaranteed to be valid at the proposed 
safe time, so, when processing the SafeTime propagation request,
+            // we'll not need to wait for Metastorage SafeTime, so processing 
will be cheap.
+            return true;
+        }
+
+        // Ok, an attempt to advance idle safe time might cause a wait on 
Metastorage SafeTime.
+        // Let's see: if Metastorage SafeTime is still not enough to avoid 
waiting on it even for our PREVIOUS attempt to advance
+        // partition SafeTime, then it makes sense to skip the current attempt 
(as the future from the previous attempt is still there
+        // and takes memory; if we make the current attempt, we are guaranteed 
to add another future). There will be next attempt
+        // to advance the partition SafeTime.
+
+        ReplicaContext context = getOrCreateContext(replica);
+
+        HybridTimestamp lastIdleSafeTimeProposal = 
context.lastIdleSafeTimeProposal;
+        if (lastIdleSafeTimeProposal == null) {
+            // No previous attempt, we have to do it ourselves.
+            return true;
+        }
+
+        // This is the Metastorage SafeTime that was needed to be achieved for 
previous attempt to check that this node is still a primary.
+        // If it's already achieved, then previous attempt is unblocked (most 
probably already finished), so we should proceed.
+        HybridTimestamp requiredMsSafeTime = 
lastIdleSafeTimeProposal.addPhysicalTime(clockService.maxClockSkewMillis());
+
+        return clusterTime.currentSafeTime().compareTo(requiredMsSafeTime) >= 
0;
+    }
+
+    private ReplicaContext getOrCreateContext(Replica replica) {
+        return contexts.computeIfAbsent(replica.groupId(), k -> new 
ReplicaContext());

Review Comment:
   Added removal of the context on replica stop



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