*** src/backend/access/heap/rewriteheap.c~	Wed May 16 19:22:55 2007
--- src/backend/access/heap/rewriteheap.c	Wed May 16 19:54:46 2007
***************
*** 292,298 ****
  /*
   * Add a tuple to the new heap.
   *
!  * Visibility information is copied from the original tuple.
   *
   * state		opaque state as returned by begin_heap_rewrite
   * old_tuple	original tuple in the old heap
--- 292,300 ----
  /*
   * Add a tuple to the new heap.
   *
!  * Visibility information is copied from the original tuple, except that
!  * we "freeze" very-old tuples.  Note that since we scribble on new_tuple,
!  * it had better be temp storage not a pointer to the original tuple.
   *
   * state		opaque state as returned by begin_heap_rewrite
   * old_tuple	original tuple in the old heap
***************
*** 324,329 ****
--- 326,342 ----
  		old_tuple->t_data->t_infomask & HEAP_XACT_MASK;
  
  	/*
+ 	 * While we have our hands on the tuple, we may as well freeze any
+ 	 * very-old xmin or xmax, so that future VACUUM effort can be saved.
+ 	 *
+ 	 * Note we abuse heap_freeze_tuple() a bit here, since it's expecting
+ 	 * to be given a pointer to a tuple in a disk buffer.  It happens
+ 	 * though that we can get the right things to happen by passing
+ 	 * InvalidBuffer for the buffer.
+ 	 */
+ 	heap_freeze_tuple(new_tuple->t_data, state->rs_oldest_xmin, InvalidBuffer);
+ 
+ 	/*
  	 * Invalid ctid means that ctid should point to the tuple itself.
  	 * We'll override it later if the tuple is part of an update chain.
  	 */
***************
*** 537,544 ****
  	Size			len;
  	OffsetNumber	newoff;
  	HeapTuple		heaptup;
- 
- 	heap_freeze_tuple(tup->t_data, state->rs_oldest_xmin, InvalidBuffer);
  
  	/*
  	 * If the new tuple is too big for storage or contains already toasted
--- 550,555 ----