Add helpful messages to the VLE subsystem (apache#1742)

Added helpful messaging to the VLE subsystem.

These changes are due to issue 365 where there was an issue with
the VLE that turned out to not be with the VLE. Basically, there
is a way, apparently, to have a malformed edge or possibly one not
fully removed. When the VLE subsystem does its load on the graph,
it would error out on these edges as this was considered to be a
potential data corruption issue.

The changes added are to report and ignore these edges. Reporting
them, so as to allow the user to take corrective action by removing
them. Ignoring them, as they are likely not relevant to the query.
Basically, leaving it up to the user to decide.

No impact to current regression tests.

Author: jrgemignani

src/backend/utils/adt/age_global_graph.c

@@ -101,7 +101,7 @@ static bool insert_edge(GRAPH_global_context *ggctx, graphid edge_id,
                         graphid end_vertex_id, Oid edge_label_table_oid);
 static bool insert_vertex_edge(GRAPH_global_context *ggctx,
                                graphid start_vertex_id, graphid end_vertex_id,
-                               graphid edge_id);
+                               graphid edge_id, char *edge_label_name);
 static bool insert_vertex_entry(GRAPH_global_context *ggctx, graphid vertex_id,
                                 Oid vertex_label_table_oid,
                                 Datum vertex_properties);
@@ -330,10 +330,11 @@ static bool insert_vertex_entry(GRAPH_global_context *ggctx, graphid vertex_id,
  */
 static bool insert_vertex_edge(GRAPH_global_context *ggctx,
                                graphid start_vertex_id, graphid end_vertex_id,
-                               graphid edge_id)
+                               graphid edge_id, char *edge_label_name)
 {
     vertex_entry *value = NULL;
-    bool found = false;
+    bool start_found = false;
+    bool end_found = false;
     bool is_selfloop = false;
 
     /* is it a self loop */
@@ -342,39 +343,70 @@ static bool insert_vertex_edge(GRAPH_global_context *ggctx,
     /* search for the start vertex of the edge */
     value = (vertex_entry *)hash_search(ggctx->vertex_hashtable,
                                         (void *)&start_vertex_id, HASH_FIND,
-                                        &found);
-    /* vertices were preloaded so it must be there */
-    Assert(found);
-    if (!found)
-    {
-        return found;
-    }
+                                        &start_found);
 
-    /* if it is a self loop, add the edge to edges_self and we're done */
-    if (is_selfloop)
+    /*
+     * If we found the start_vertex_id and it is a self loop, add the edge to
+     * edges_self and we're done
+     */
+    if (start_found && is_selfloop)
     {
         value->edges_self = append_graphid(value->edges_self, edge_id);
-        return found;
+        return true;
+    }
+    /*
+     * Otherwise, if we found the start_vertex_id add the edge to the edges_out
+     * list of the start vertex
+     */
+    else if (start_found)
+    {
+        value->edges_out = append_graphid(value->edges_out, edge_id);
     }
-
-    /* add the edge to the edges_out list of the start vertex */
-    value->edges_out = append_graphid(value->edges_out, edge_id);
 
     /* search for the end vertex of the edge */
     value = (vertex_entry *)hash_search(ggctx->vertex_hashtable,
                                         (void *)&end_vertex_id, HASH_FIND,
-                                        &found);
-    /* vertices were preloaded so it must be there */
-    Assert(found);
-    if (!found)
+                                        &end_found);
+
+    /*
+     * If we found the start_vertex_id and the end_vertex_id add the edge to the
+     * edges_in list of the end vertex
+     */
+    if (start_found && end_found)
     {
-        return found;
+        value->edges_in = append_graphid(value->edges_in, edge_id);
+        return true;
+    }
+    /*
+     * Otherwise we need to generate the appropriate warning message about the
+     * dangling edge that we found.
+     */
+    else if (!start_found && end_found)
+    {
+        ereport(WARNING,
+                (errcode(ERRCODE_DATA_EXCEPTION),
+                 errmsg("edge: [id: %ld, start: %ld, end: %ld, label: %s] %s",
+                        edge_id, start_vertex_id, end_vertex_id,
+                        edge_label_name, "start vertex not found")));
+    }
+    else if (start_found && !end_found)
+    {
+        ereport(WARNING,
+                (errcode(ERRCODE_DATA_EXCEPTION),
+                 errmsg("edge: [id: %ld, start: %ld, end: %ld, label: %s] %s",
+                        edge_id, start_vertex_id, end_vertex_id,
+                        edge_label_name, "end vertex not found")));
+    }
+    else
+    {
+        ereport(WARNING,
+                (errcode(ERRCODE_DATA_EXCEPTION),
+                 errmsg("edge: [id: %ld, start: %ld, end: %ld, label: %s] %s",
+                        edge_id, start_vertex_id, end_vertex_id,
+                        edge_label_name, "start and end vertices not found")));
     }
 
-    /* add the edge to the edges_in list of the end vertex */
-    value->edges_in = append_graphid(value->edges_in, edge_id);
-
-    return found;
+    return false;
 }
 
 /* helper routine to load all vertices into the GRAPH global vertex hashtable */
@@ -430,7 +462,12 @@ static void load_vertex_hashtable(GRAPH_global_context *ggctx)
             bool inserted = false;
 
             /* something is wrong if this isn't true */
+            if (!HeapTupleIsValid(tuple))
+            {
+                elog(ERROR, "load_vertex_hashtable: !HeapTupleIsValid");
+            }
             Assert(HeapTupleIsValid(tuple));
+
             /* get the vertex id */
             vertex_id = DatumGetInt64(column_get_datum(tupdesc, tuple, 0, "id",
                                                        GRAPHIDOID, true));
@@ -533,7 +570,12 @@ static void load_edge_hashtable(GRAPH_global_context *ggctx)
             bool inserted = false;
 
             /* something is wrong if this isn't true */
+            if (!HeapTupleIsValid(tuple))
+            {
+                elog(ERROR, "load_edge_hashtable: !HeapTupleIsValid");
+            }
             Assert(HeapTupleIsValid(tuple));
+
             /* get the edge id */
             edge_id = DatumGetInt64(column_get_datum(tupdesc, tuple, 0, "id",
                                                      GRAPHIDOID, true));
@@ -568,11 +610,13 @@ static void load_edge_hashtable(GRAPH_global_context *ggctx)
 
             /* insert the edge into the start and end vertices edge lists */
             inserted = insert_vertex_edge(ggctx, edge_vertex_start_id,
-                                          edge_vertex_end_id, edge_id);
-            /* this insert must not fail */
+                                          edge_vertex_end_id, edge_id,
+                                          edge_label_name);
             if (!inserted)
             {
-                 elog(ERROR, "insert_vertex_edge: failed to insert");
+                 ereport(WARNING,
+                         (errcode(ERRCODE_DATA_EXCEPTION),
+                          errmsg("ignored malformed or dangling edge")));
             }
         }