sqldb+graph/db: prune graph nodes in a single query

Update the pruneGraphNodes routine to prune the graph nodes in a single
query instead of two.

graph/db/sql_store.go

@@ -64,7 +64,7 @@ type SQLQueries interface {
 	ListNodesPaginated(ctx context.Context, arg sqlc.ListNodesPaginatedParams) ([]sqlc.Node, error)
 	ListNodeIDsAndPubKeys(ctx context.Context, arg sqlc.ListNodeIDsAndPubKeysParams) ([]sqlc.ListNodeIDsAndPubKeysRow, error)
 	IsPublicV1Node(ctx context.Context, pubKey []byte) (bool, error)
-	GetUnconnectedNodes(ctx context.Context) ([]sqlc.GetUnconnectedNodesRow, error)
+	DeleteUnconnectedNodes(ctx context.Context) ([][]byte, error)
 	DeleteNodeByPubKey(ctx context.Context, arg sqlc.DeleteNodeByPubKeyParams) (sql.Result, error)
 	DeleteNode(ctx context.Context, id int64) error
 
@@ -2551,30 +2551,21 @@ func (s *SQLStore) PruneTip() (*chainhash.Hash, uint32, error) {
 func (s *SQLStore) pruneGraphNodes(ctx context.Context,
 	db SQLQueries) ([]route.Vertex, error) {
 
-	// Fetch all un-connected nodes from the database.
-	// NOTE: this will not include any nodes that are listed in the
-	// source table.
-	nodes, err := db.GetUnconnectedNodes(ctx)
+	nodeKeys, err := db.DeleteUnconnectedNodes(ctx)
 	if err != nil {
-		return nil, fmt.Errorf("unable to fetch unconnected nodes: %w",
-			err)
+		return nil, fmt.Errorf("unable to delete unconnected "+
+			"nodes: %w", err)
 	}
 
-	prunedNodes := make([]route.Vertex, 0, len(nodes))
-	for _, node := range nodes {
-		// TODO(elle): update to use sqlc.slice() once that works.
-		if err = db.DeleteNode(ctx, node.ID); err != nil {
-			return nil, fmt.Errorf("unable to delete "+
-				"node(id=%d): %w", node.ID, err)
-		}
-
-		pubKey, err := route.NewVertexFromBytes(node.PubKey)
+	prunedNodes := make([]route.Vertex, len(nodeKeys))
+	for i, nodeKey := range nodeKeys {
+		pub, err := route.NewVertexFromBytes(nodeKey)
 		if err != nil {
 			return nil, fmt.Errorf("unable to parse pubkey "+
-				"for node(id=%d): %w", node.ID, err)
+				"from bytes: %w", err)
 		}
 
-		prunedNodes = append(prunedNodes, pubKey)
+		prunedNodes[i] = pub
 	}
 
 	return prunedNodes, nil