MB-34017: Correct Disk snapshot marker to not send 0 value

A Disk snapshot will now send a HCS value from the active node to
the replica node. This value could be 0 if no SyncWrites have been
completed. If this is the case, we should not send a 0 HCS as there
is no need and it will cause a pre-condition to fail in the flusher
on the replica.

Change-Id: Ic0708ee4df90d2b1d2fe9f6879fb58838738255f
Reviewed-on: http://review.couchbase.org/113492
Reviewed-by: Dave Rigby <[email protected]>
Tested-by: Build Bot <[email protected]>

Author: BenHuddleston

daemon/protocol/mcbp/dcp_snapshot_marker_executor.cc

@@ -40,6 +40,14 @@ void dcp_snapshot_marker_executor(Cookie& cookie) {
             const auto* v2Payload =
                     reinterpret_cast<const DcpSnapshotMarkerV2Payload*>(
                             extra.data());
+
+            // HCS should never be sent as 0 or a pre-condition will throw in
+            // the replicas flusher
+            if (v2Payload->getHighCompletedSeqno() == 0) {
+                // Not success so just disconnect
+                connection.setState(StateMachine::State::closing);
+                return;
+            }
             hcs = v2Payload->getHighCompletedSeqno();
         }
 

engines/ep/src/dcp/active_stream.cc

@@ -295,14 +295,16 @@ void ActiveStream::markDiskSnapshot(
             startSeqno,
             endSeqno);
         // If the stream supports SyncRep then send the HCS in the
-        // SnapshotMarker
+        // SnapshotMarker if it is not 0
+        auto sendHCS = supportSyncReplication() && highCompletedSeqno &&
+                       *highCompletedSeqno != 0;
         pushToReadyQ(std::make_unique<SnapshotMarker>(
                 opaque_,
                 vb_,
                 startSeqno,
                 endSeqno,
                 MARKER_FLAG_DISK | MARKER_FLAG_CHK,
-                supportSyncReplication() ? highCompletedSeqno : boost::none,
+                sendHCS ? highCompletedSeqno : boost::none,
                 sid));
         lastSentSnapEndSeqno.store(endSeqno, std::memory_order_relaxed);