fix: handle stale TID in VLE path materialization after DETACH DELETE (#2549)

regress/expected/cypher_vle.out

@@ -1334,6 +1334,52 @@ NOTICE:  graph "issue_2382" has been dropped
 
 (1 row)
 
+--
+-- Issue #2549: VLE path + DETACH DELETE + RETURN p should not raise
+-- stale TID error.  When the path's bound vertices are deleted before
+-- the path datum is materialized, build_path must tolerate the stale
+-- TID and return the path with empty properties ({}) for the deleted
+-- entities.
+--
+SELECT create_graph('issue_2549');
+NOTICE:  graph "issue_2549" has been created
+ create_graph 
+--------------
+
+(1 row)
+
+SELECT * FROM cypher('issue_2549', $$
+    CREATE (a {id: 1})<-[:R]-(b {id: 2}),
+           (a)<-[:R]-(c {id: 3})
+    RETURN a
+$$) AS (v agtype);
+                                   v                                   
+-----------------------------------------------------------------------
+ {"id": 281474976710657, "label": "", "properties": {"id": 1}}::vertex
+(1 row)
+
+SELECT * FROM cypher('issue_2549', $$
+    MATCH p = (n0)<-[:R*..2]-(n1)
+    DETACH DELETE n0, n1
+    RETURN p
+$$) AS (p agtype);
+                                                                                                                                                      p                                                                                                                                                      
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ [{"id": 281474976710657, "label": "_ag_label_vertex", "properties": {"id": 1}}::vertex, {"id": 844424930131970, "label": "R", "end_id": 281474976710657, "start_id": 281474976710659, "properties": {}}::edge, {"id": 281474976710659, "label": "_ag_label_vertex", "properties": {"id": 3}}::vertex]::path
+ [{"id": 281474976710657, "label": "_ag_label_vertex", "properties": {}}::vertex, {"id": 844424930131969, "label": "R", "end_id": 281474976710657, "start_id": 281474976710658, "properties": {}}::edge, {"id": 281474976710658, "label": "_ag_label_vertex", "properties": {"id": 2}}::vertex]::path
+(2 rows)
+
+SELECT drop_graph('issue_2549', true);
+NOTICE:  drop cascades to 3 other objects
+DETAIL:  drop cascades to table issue_2549._ag_label_vertex
+drop cascades to table issue_2549._ag_label_edge
+drop cascades to table issue_2549."R"
+NOTICE:  graph "issue_2549" has been dropped
+ drop_graph 
+------------
+
+(1 row)
+
 --
 -- End
 --

regress/sql/cypher_vle.sql

@@ -487,6 +487,26 @@ $$) AS (person agtype, friend agtype);
 
 SELECT drop_graph('issue_2382', true);
 
+--
+-- Issue #2549: VLE path + DETACH DELETE + RETURN p should not raise
+-- stale TID error.  When the path's bound vertices are deleted before
+-- the path datum is materialized, build_path must tolerate the stale
+-- TID and return the path with empty properties ({}) for the deleted
+-- entities.
+--
+SELECT create_graph('issue_2549');
+SELECT * FROM cypher('issue_2549', $$
+    CREATE (a {id: 1})<-[:R]-(b {id: 2}),
+           (a)<-[:R]-(c {id: 3})
+    RETURN a
+$$) AS (v agtype);
+SELECT * FROM cypher('issue_2549', $$
+    MATCH p = (n0)<-[:R*..2]-(n1)
+    DETACH DELETE n0, n1
+    RETURN p
+$$) AS (p agtype);
+SELECT drop_graph('issue_2549', true);
+
 --
 -- End
 --

src/backend/utils/adt/age_global_graph.c

@@ -41,6 +41,7 @@
 
 #include "utils/age_global_graph.h"
 #include "utils/agehash.h"
+#include "utils/agtype.h"
 #include "catalog/ag_graph.h"
 #include "catalog/ag_label.h"
 #include "utils/ag_cache.h"
@@ -1426,6 +1427,74 @@ Datum get_vertex_entry_properties(vertex_entry *ve)
     return result;
 }
 
+/*
+ * Tolerant variant of get_vertex_entry_properties used by the VLE path
+ * materializer.
+ *
+ * The VLE SRF stores paths as interleaved graphid arrays and only lazily
+ * fetches vertex properties when the path datum is projected (build_path).
+ * When the path's bound vertices were deleted earlier in the same query
+ * (e.g. `MATCH p = ... DETACH DELETE ... RETURN p`), the stored TID no
+ * longer resolves to a visible tuple. The non-VLE path executor builds its
+ * path datums eagerly (before DELETE runs), so it never hits this case;
+ * build_path must tolerate it instead of raising an internal error.
+ *
+ * Returns an empty agtype object ({}) as the properties when the tuple is
+ * no longer visible, so the path can still be projected with the vertex
+ * present but its properties empty.
+ */
+Datum get_vertex_entry_properties_graceful(vertex_entry *ve)
+{
+    Relation rel;
+    HeapTupleData tuple;
+    Buffer buffer = InvalidBuffer;
+    Datum result = (Datum) 0;
+
+    rel = table_open(ve->vertex_label_table_oid, AccessShareLock);
+    tuple.t_self = ve->tid;
+
+    if (heap_fetch(rel, GetActiveSnapshot(), &tuple, &buffer, true))
+    {
+        TupleDesc tupdesc = RelationGetDescr(rel);
+        bool isnull;
+        Datum props;
+
+        /* properties is column 2 (1-indexed) */
+        props = heap_getattr(&tuple, 2, tupdesc, &isnull);
+        if (!isnull)
+        {
+            result = datumCopy(props, false, -1);
+        }
+
+        ReleaseBuffer(buffer);
+        buffer = InvalidBuffer;
+    }
+
+    table_close(rel, AccessShareLock);
+
+    /* defensive: release any leftover pin (PG 18 heap_fetch may pin
+     * buffer in some failure paths) */
+    if (BufferIsValid(buffer))
+        ReleaseBuffer(buffer);
+
+    if (result == (Datum) 0)
+    {
+        agtype_in_state result_state;
+
+        /* build an empty object ({}) as the properties */
+        memset(&result_state, 0, sizeof(agtype_in_state));
+        push_agtype_value(&result_state.parse_state, WAGT_BEGIN_OBJECT, NULL);
+        result_state.res = push_agtype_value(&result_state.parse_state,
+                                             WAGT_END_OBJECT, NULL);
+
+        result = AGTYPE_P_GET_DATUM(agtype_value_to_agtype(result_state.res));
+
+        pfree_agtype_in_state(&result_state);
+    }
+
+    return result;
+}
+
 /* edge_entry accessor functions */
 graphid get_edge_entry_id(edge_entry *ee)
 {
@@ -1486,6 +1555,65 @@ Datum get_edge_entry_properties(edge_entry *ee)
     return result;
 }
 
+/*
+ * Tolerant variant of get_edge_entry_properties used by the VLE path
+ * materializer. See get_vertex_entry_properties_graceful for rationale:
+ * when the path's bound edges were deleted earlier in the same query, the
+ * stored TID no longer resolves to a visible tuple, and the path must be
+ * projectable with an empty properties object ({}) instead of raising an
+ * internal error.
+ */
+Datum get_edge_entry_properties_graceful(edge_entry *ee)
+{
+    Relation rel;
+    HeapTupleData tuple;
+    Buffer buffer = InvalidBuffer;
+    Datum result = (Datum) 0;
+
+    rel = table_open(ee->edge_label_table_oid, AccessShareLock);
+    tuple.t_self = ee->tid;
+
+    if (heap_fetch(rel, GetActiveSnapshot(), &tuple, &buffer, true))
+    {
+        TupleDesc tupdesc = RelationGetDescr(rel);
+        bool isnull;
+        Datum props;
+
+        /* properties is column 4 (1-indexed) */
+        props = heap_getattr(&tuple, 4, tupdesc, &isnull);
+        if (!isnull)
+        {
+            result = datumCopy(props, false, -1);
+        }
+
+        ReleaseBuffer(buffer);
+        buffer = InvalidBuffer;
+    }
+
+    table_close(rel, AccessShareLock);
+
+    /* defensive: release any leftover pin */
+    if (BufferIsValid(buffer))
+        ReleaseBuffer(buffer);
+
+    if (result == (Datum) 0)
+    {
+        agtype_in_state result_state;
+
+        /* build an empty object ({}) as the properties */
+        memset(&result_state, 0, sizeof(agtype_in_state));
+        push_agtype_value(&result_state.parse_state, WAGT_BEGIN_OBJECT, NULL);
+        result_state.res = push_agtype_value(&result_state.parse_state,
+                                             WAGT_END_OBJECT, NULL);
+
+        result = AGTYPE_P_GET_DATUM(agtype_value_to_agtype(result_state.res));
+
+        pfree_agtype_in_state(&result_state);
+    }
+
+    return result;
+}
+
 graphid get_edge_entry_start_vertex_id(edge_entry *ee)
 {
     return ee->start_vertex_id;

src/backend/utils/adt/age_vle.c

@@ -1782,7 +1782,7 @@ static agtype_value *build_edge_list(VLE_path_container *vpc)
         agtv_edge = agtype_value_build_edge(get_edge_entry_id(ee), label_name,
                                             get_edge_entry_end_vertex_id(ee),
                                             get_edge_entry_start_vertex_id(ee),
-                                            get_edge_entry_properties(ee));
+                                            get_edge_entry_properties_graceful(ee));
         /* push the edge*/
         edges_result.res = push_agtype_value(&edges_result.parse_state,
                                              WAGT_ELEM, agtv_edge);
@@ -1847,7 +1847,7 @@ static agtype_value *build_path(VLE_path_container *vpc)
         /* reconstruct the vertex */
         agtv_vertex = agtype_value_build_vertex(get_vertex_entry_id(ve),
                                                 label_name,
-                                                get_vertex_entry_properties(ve));
+                                                get_vertex_entry_properties_graceful(ve));
         /* push the vertex */
         path_result.res = push_agtype_value(&path_result.parse_state, WAGT_ELEM,
                                             agtv_vertex);
@@ -1869,7 +1869,7 @@ static agtype_value *build_path(VLE_path_container *vpc)
         agtv_edge = agtype_value_build_edge(get_edge_entry_id(ee), label_name,
                                             get_edge_entry_end_vertex_id(ee),
                                             get_edge_entry_start_vertex_id(ee),
-                                            get_edge_entry_properties(ee));
+                                            get_edge_entry_properties_graceful(ee));
         /* push the edge*/
         path_result.res = push_agtype_value(&path_result.parse_state, WAGT_ELEM,
                                             agtv_edge);

src/include/utils/age_global_graph.h

@@ -77,6 +77,11 @@ edge_entry *get_edge_entry_with_hash(GRAPH_global_context *ggctx,
 graphid get_vertex_entry_id(vertex_entry *ve);
 Oid get_vertex_entry_label_table_oid(vertex_entry *ve);
 Datum get_vertex_entry_properties(vertex_entry *ve);
+/* tolerant variants for VLE path materialization: return empty object ({})
+ * when the referenced tuple is no longer visible instead of raising
+ * a stale-TID error (see age_vle.c build_path) */
+Datum get_vertex_entry_properties_graceful(vertex_entry *ve);
+Datum get_edge_entry_properties_graceful(edge_entry *ee);
 
 /*
  * Flat-array adjacency accessors. Returned pointer is into the entry's