fix(graphrag): stop losing chunks silently during a graph build

Three ways a chunk disappeared from a graph with no way to tell:

A build checks out one connection and then spends minutes per chunk waiting
on the model, so the connection idles long enough for the server or a pooler
to drop it. The pool only validates a connection when it hands one out, and
this one was handed out at the start of the build, so the next write raised
"the connection is lost", the chunk was marked failed, and the build carried
on a chunk short. apply_chunk and mark_chunk now reconnect and retry once;
every statement they run is an idempotent upsert, so a replay cannot
double-write. Only connection loss retries — a bad statement still surfaces.

An unparseable model response marked the chunk failed and logged nothing at
all, so failed_chunks was the only evidence and it named no chunk. Both
failure modes now log the chunk id.

The summary's node count summed per-chunk upserts, so an entity appearing in
ten chunks counted ten times: it reported writes, not graph size. It now
reports the distinct node count, falling back to the write count only if the
count query fails.

docsgpt/graphrag/store.py

@@ -17,6 +17,7 @@ import logging
 import uuid
 from typing import Any, Dict, List, Optional
 
+import psycopg
 from psycopg.types.json import Jsonb
 
 from docsgpt.core.settings import settings
@@ -73,6 +74,25 @@ def _pgvector_identifiers() -> tuple[str, str, str, str]:
     )
 
 
+def _is_connection_lost(exc: BaseException) -> bool:
+    """True when ``exc`` says the server connection went away, not that the SQL was bad.
+
+    psycopg raises ``OperationalError`` ("the connection is lost") when the
+    socket dies under a statement and ``InterfaceError`` when the connection
+    object is already closed. Everything else — a bad statement, a constraint
+    violation — is a real failure that a retry would only repeat.
+    """
+    return isinstance(exc, (psycopg.OperationalError, psycopg.InterfaceError))
+
+
+def _safe_rollback(conn) -> None:
+    """Roll back, tolerating a connection too broken to roll back."""
+    try:
+        conn.rollback()
+    except Exception as exc:
+        logging.debug("Rollback on a broken connection failed: %s", exc)
+
+
 class GraphStore:
     """Stores and queries a per-source knowledge graph in the pgvector DB."""
 
@@ -138,6 +158,37 @@ class GraphStore:
                 self._pooled = False
         return self._connection
 
+    def _write_with_reconnect(self, operation):
+        """Run ``operation(conn)``, once more on a fresh connection if it was dead.
+
+        A graph build holds one checked-out connection for the length of the
+        whole extraction and spends minutes per chunk waiting on the model, so
+        the connection idles long enough for the server (or a pooler) to drop
+        it. The pool only validates a connection when it is handed out, and
+        this one was handed out at the start of the build, so the next write
+        raises and its chunk is lost from the graph. Every statement here is an
+        idempotent upsert, so replaying one on a new connection cannot
+        double-write.
+
+        Args:
+            operation: Callable taking the connection and doing one write.
+
+        Returns:
+            Whatever ``operation`` returns.
+        """
+        for attempt in (1, 2):
+            conn = self._get_connection()
+            try:
+                return operation(conn)
+            except Exception as exc:
+                if attempt == 2 or not _is_connection_lost(exc):
+                    raise
+                logging.warning(
+                    "Graph write lost its connection (%s); reconnecting and retrying once.",
+                    exc,
+                )
+                self.close()
+
     def _register_pgvector_types(self, conn) -> None:
         """Register pgvector's adapters, tolerating a not-yet-created extension.
 
@@ -499,56 +550,61 @@ class GraphStore:
         (not linked to the chunk), mirroring the per-call path.
         ``name_embeddings`` maps ``normalized_name`` to its embedding. Degrees
         are not bumped here — the caller runs ``set_node_degrees`` once at the
-        end. Returns ``(nodes_upserted, edges_added)``.
+        end. Reconnects and retries once if the connection died while the
+        extraction was waiting on the model. Returns
+        ``(nodes_upserted, edges_added)``.
         """
         self._ensure_tables_once()
-        conn = self._get_connection()
-        cursor = conn.cursor()
-        node_ids: Dict[str, str] = {}
-        edges_added = 0
-        try:
-            for entity in entities:
-                normalized_name = entity["normalized_name"]
-                node_id = self._upsert_node(
-                    cursor,
-                    source_id,
-                    entity["name"],
-                    normalized_name,
-                    entity.get("type"),
-                    entity.get("description"),
-                    name_embeddings.get(normalized_name),
-                )
-                node_ids[normalized_name] = node_id
-                self._link_node_chunk(cursor, source_id, node_id, chunk_id)
 
-            for rel in relationships:
-                src_id = self._resolve_endpoint(
-                    cursor, source_id, rel.get("source"), node_ids, name_embeddings
-                )
-                dst_id = self._resolve_endpoint(
-                    cursor, source_id, rel.get("target"), node_ids, name_embeddings
-                )
-                if src_id is None or dst_id is None:
-                    continue
-                self._add_edge(
-                    cursor,
-                    source_id,
-                    src_id,
-                    dst_id,
-                    type=rel.get("type"),
-                    description=rel.get("description"),
-                    weight=float(rel.get("weight") or 1.0),
-                    source_chunk_ids=[chunk_id],
-                )
-                edges_added += 1
+        def _write(conn):
+            cursor = conn.cursor()
+            node_ids: Dict[str, str] = {}
+            edges_added = 0
+            try:
+                for entity in entities:
+                    normalized_name = entity["normalized_name"]
+                    node_id = self._upsert_node(
+                        cursor,
+                        source_id,
+                        entity["name"],
+                        normalized_name,
+                        entity.get("type"),
+                        entity.get("description"),
+                        name_embeddings.get(normalized_name),
+                    )
+                    node_ids[normalized_name] = node_id
+                    self._link_node_chunk(cursor, source_id, node_id, chunk_id)
 
-            conn.commit()
-            return len(entities), edges_added
-        except Exception:
-            conn.rollback()
-            raise
-        finally:
-            cursor.close()
+                for rel in relationships:
+                    src_id = self._resolve_endpoint(
+                        cursor, source_id, rel.get("source"), node_ids, name_embeddings
+                    )
+                    dst_id = self._resolve_endpoint(
+                        cursor, source_id, rel.get("target"), node_ids, name_embeddings
+                    )
+                    if src_id is None or dst_id is None:
+                        continue
+                    self._add_edge(
+                        cursor,
+                        source_id,
+                        src_id,
+                        dst_id,
+                        type=rel.get("type"),
+                        description=rel.get("description"),
+                        weight=float(rel.get("weight") or 1.0),
+                        source_chunk_ids=[chunk_id],
+                    )
+                    edges_added += 1
+
+                conn.commit()
+                return len(entities), edges_added
+            except Exception:
+                _safe_rollback(conn)
+                raise
+            finally:
+                cursor.close()
+
+        return self._write_with_reconnect(_write)
 
     def _resolve_endpoint(
         self,
@@ -1026,25 +1082,29 @@ class GraphStore:
             cursor.close()
 
     def mark_chunk(self, source_id: str, chunk_id: str, status: str):
+        """Record a chunk's extraction status, reconnecting once if the connection died."""
         self._ensure_tables_once()
-        conn = self._get_connection()
-        cursor = conn.cursor()
-        try:
-            cursor.execute(
-                """
-                INSERT INTO graph_ingest_progress (source_id, chunk_id, status)
-                VALUES (%s, %s, %s)
-                ON CONFLICT (source_id, chunk_id) DO UPDATE SET status = EXCLUDED.status;
-                """,
-                (source_id, str(chunk_id), status),
-            )
-            conn.commit()
-        except Exception as e:
-            conn.rollback()
-            logging.error(f"Error marking chunk: {e}")
-            raise
-        finally:
-            cursor.close()
+
+        def _write(conn):
+            cursor = conn.cursor()
+            try:
+                cursor.execute(
+                    """
+                    INSERT INTO graph_ingest_progress (source_id, chunk_id, status)
+                    VALUES (%s, %s, %s)
+                    ON CONFLICT (source_id, chunk_id) DO UPDATE SET status = EXCLUDED.status;
+                    """,
+                    (source_id, str(chunk_id), status),
+                )
+                conn.commit()
+            except Exception as e:
+                _safe_rollback(conn)
+                logging.error(f"Error marking chunk: {e}")
+                raise
+            finally:
+                cursor.close()
+
+        return self._write_with_reconnect(_write)
 
     def pending_chunks(self, source_id: str, all_chunk_ids: List[str]) -> List[str]:
         """Chunk ids from ``all_chunk_ids`` not yet marked ``done`` for the source."""