typedef struct MemoryContextData
{
	NodeTag		type;			/* identifies exact kind of context */
	MemoryContextMethods methods;		/* virtual function table */
	MemoryContext parent;		/* NULL if no parent (toplevel context) */
	MemoryContext firstchild;	/* head of linked list of children */
	MemoryContext nextchild;	/* next child of same parent */
	char	   *name;			/* context name (just for debugging) */
	bool		isReset;		/* T = no space alloced since last reset */

  /* CDB: Lifetime cumulative stats for this context and all descendants */
  ……
} MemoryContextData;

typedef struct MemoryContextData *MemoryContext;