Fixed wrong log message when removing temporary part after merge, that is not...

Fixed wrong log message when removing temporary part after merge, that is not byte-identical than same part on replicas; added profile event; added fail-safe logic [#MTRSADMIN-3175].

dbms/src/Common/ProfileEvents.cpp

@@ -122,6 +122,8 @@
     M(DictCacheRequests) \
     M(DictCacheLockWriteNs) \
     M(DictCacheLockReadNs) \
+    \
+    M(DataAfterMergeDiffersFromReplica)
 
 
 namespace ProfileEvents

dbms/src/Storages/MergeTree/MergeTreeDataPart.cpp

@@ -374,6 +374,9 @@ size_t MergeTreeDataPart::getExactSizeRows() const
 
 String MergeTreeDataPart::getFullPath() const
 {
+    if (relative_path.empty())
+        throw Exception("Part relative_path cannot be empty. This is bug.", ErrorCodes::LOGICAL_ERROR);
+
     return storage.full_path + relative_path + "/";
 }
 
@@ -431,7 +434,10 @@ size_t MergeTreeDataPart::calcTotalSize(const String & from)
 
 void MergeTreeDataPart::remove() const
 {
-    String from = storage.full_path + name;
+    if (relative_path.empty())
+        throw Exception("Part relative_path cannot be empty. This is bug.", ErrorCodes::LOGICAL_ERROR);
+
+    String from = storage.full_path + relative_path;
     String to = storage.full_path + "tmp_delete_" + name;
 
     Poco::File from_dir{from};

dbms/src/Storages/StorageReplicatedMergeTree.cpp

@@ -56,6 +56,7 @@ namespace ProfileEvents
     extern const Event ReplicatedPartFetchesOfMerged;
     extern const Event ObsoleteReplicatedParts;
     extern const Event ReplicatedPartFetches;
+    extern const Event DataAfterMergeDiffersFromReplica;
 }
 
 namespace DB
@@ -1093,6 +1094,8 @@ bool StorageReplicatedMergeTree::executeLogEntry(const LogEntry & entry)
                     do_fetch = true;
                     part->remove();
 
+                    ProfileEvents::increment(ProfileEvents::DataAfterMergeDiffersFromReplica);
+
                     LOG_ERROR(log, getCurrentExceptionMessage(false) << ". "
                         "Data after merge is not byte-identical to data on another replicas. "
                         "There could be several reasons: "