if a node sends a Prepare and it is behind we send it a Fixed as well…

… as the nack.
trex-paxos · Dec 14, 2024 · 023dc58 · 023dc58
1 parent b1213db
commit 023dc58
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diff --git a/trex2-lib/src/main/java/com/github/trex_paxos/TrexNode.java b/trex2-lib/src/main/java/com/github/trex_paxos/TrexNode.java
@@ -244,6 +244,12 @@ private void algorithm(TrexMessage input,
         if (number.lessThan(progress.highestPromised()) || logIndex <= progress.highestFixedIndex()) {
           // nack a low nextPrepareMessage else any nextPrepareMessage for a fixed slot sending any accepts they are missing
           messages.add(nack(prepare));
+          // if the other node is behind tell them that the slot is fixed. this will force them to catchup.
+          if( logIndex < progress.highestFixedIndex() ) {
+            journal.readAccept(progress.highestFixedIndex())
+                .ifPresent(fixedAccept ->
+                    messages.add(new Fixed(nodeIdentifier, fixedAccept.slot(), fixedAccept.number())));
+          }
         } else if (number.greaterThan(progress.highestPromised())) {
           // ack a higher nextPrepareMessage
           final var newProgress = progress.withHighestPromised(number);
@@ -320,9 +326,9 @@ case Catchup(final byte replyTo, _, final var otherFixedIndex, final var otherHi
 
         /// If the other node has seen a higher promise then we must increase our term
         /// to be higher. We do not update our promise as we would be doing that in a learning
-        ///  message which is not part of the protocol. Instead, we bump or term. Next time we
-        ///  produce an `accept` we will use our term and do a self accept to that which will
-        ///  bump pur promise. We do not want to alter the promise when not an `accept` or `prepare` message.
+        /// message which is not part of the protocol. Instead, we bump or term. Next time we
+        /// produce an `accept` we will use our term and do a self accept to that which will
+        /// bump pur promise. We do not want to alter the promise when not an `accept` or `prepare` message.
         if (otherHighestPromised.greaterThan(progress.highestPromised())) {
           if (role == TrexRole.LEAD) {
             assert this.term != null;

diff --git a/trex2-lib/src/test/java/com/github/trex_paxos/PreparePropertyTests.java b/trex2-lib/src/test/java/com/github/trex_paxos/PreparePropertyTests.java
@@ -102,7 +102,7 @@ public Optional<Accept> readAccept(long logIndex) {
       assert commands.isEmpty();
 
       // Should get either nothing or a single prepare response.
-      assert messages.size() <= 1;
+      assert messages.size() <= 2;
 
       // Verify response
       if (!messages.isEmpty()) {
@@ -134,6 +134,13 @@ public Optional<Accept> readAccept(long logIndex) {
             assert response.journaledAccept().isEmpty();
           }
         }
+
+        if( messages.size() == 2 ) {
+          assert testCase.fixedSlotRelation == ArbitraryValues.FixedSlotRelation.LESS;
+          var fixed = (Fixed) messages.getLast();
+          assert fixed.from() == nodeId;
+          assert fixed.slot() == otherIndex;
+        }
       }
 
       // Verify role changes
@@ -148,6 +155,7 @@ public Optional<Accept> readAccept(long logIndex) {
   /// Provides test cases covering all combinations of relationships between
   /// the node under test and the prepare message properties
   @Provide
+  @SuppressWarnings("unused")
   Arbitrary<TestCase> testCases() {
     return Combinators.combine(
         Arbitraries.of(ArbitraryValues.RoleState.values()),