Index: vacuum.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/commands/vacuum.c,v
retrieving revision 1.348
diff -c -r1.348 vacuum.c
*** vacuum.c	13 Mar 2007 00:33:40 -0000	1.348
--- vacuum.c	13 Mar 2007 18:00:14 -0000
***************
*** 1880,1885 ****
--- 1880,1894 ----
  			 * To be on the safe side, we abandon the repair_frag process if
  			 * we cannot find the parent tuple in vtlinks.	This may be overly
  			 * conservative; AFAICS it would be safe to move the chain.
+ 			 *
+ 			 * Also, because we distinguish DEAD and RECENTLY_DEAD tuples
+ 			 * using OldestXmin, which is a rather coarse test, it is quite
+ 			 * possible to have an update chain in which a tuple we think is
+ 			 * RECENTLY_DEAD links forward to one that is definitely DEAD.
+ 			 * In such a case the RECENTLY_DEAD tuple must actually be dead,
+ 			 * but it seems too complicated to try to make VACUUM remove it.
+ 			 * We treat each contiguous set of RECENTLY_DEAD tuples as a
+ 			 * separately movable chain, ignoring any intervening DEAD ones.
  			 */
  			if (((tuple.t_data->t_infomask & HEAP_UPDATED) &&
  				 !TransactionIdPrecedes(HeapTupleHeaderGetXmin(tuple.t_data),
***************
*** 1892,1897 ****
--- 1901,1907 ----
  				Buffer		Cbuf = buf;
  				bool		freeCbuf = false;
  				bool		chain_move_failed = false;
+ 				bool		moved_target = false;
  				ItemPointerData Ctid;
  				HeapTupleData tp = tuple;
  				Size		tlen = tuple_len;
***************
*** 1919,1925 ****
  				 * If this tuple is in the begin/middle of the chain then we
  				 * have to move to the end of chain.  As with any t_ctid
  				 * chase, we have to verify that each new tuple is really the
! 				 * descendant of the tuple we came from.
  				 */
  				while (!(tp.t_data->t_infomask & (HEAP_XMAX_INVALID |
  												  HEAP_IS_LOCKED)) &&
--- 1929,1941 ----
  				 * If this tuple is in the begin/middle of the chain then we
  				 * have to move to the end of chain.  As with any t_ctid
  				 * chase, we have to verify that each new tuple is really the
! 				 * descendant of the tuple we came from; however, here we
! 				 * need even more than the normal amount of paranoia.
! 				 * If t_ctid links forward to a tuple determined to be DEAD,
! 				 * then depending on where that tuple is, it might already
! 				 * have been removed, and perhaps even replaced by a MOVED_IN
! 				 * tuple.  We don't want to include any DEAD tuples in the
! 				 * chain, so we have to recheck HeapTupleSatisfiesVacuum.
  				 */
  				while (!(tp.t_data->t_infomask & (HEAP_XMAX_INVALID |
  												  HEAP_IS_LOCKED)) &&
***************
*** 1933,1938 ****
--- 1949,1955 ----
  					OffsetNumber nextOffnum;
  					ItemId		nextItemid;
  					HeapTupleHeader nextTdata;
+ 					HTSV_Result	nextTstatus;
  
  					nextTid = tp.t_data->t_ctid;
  					priorXmax = HeapTupleHeaderGetXmax(tp.t_data);
***************
*** 1963,1968 ****
--- 1980,1998 ----
  						ReleaseBuffer(nextBuf);
  						break;
  					}
+ 					/* must check for DEAD or MOVED_IN tuple, too */
+ 					nextTstatus = HeapTupleSatisfiesVacuum(nextTdata,
+ 														   OldestXmin,
+ 														   nextBuf);
+ 					if (nextTstatus == HEAPTUPLE_DEAD ||
+ 						nextTstatus == HEAPTUPLE_INSERT_IN_PROGRESS)
+ 					{
+ 						ReleaseBuffer(nextBuf);
+ 						break;
+ 					}
+ 					/* if it's MOVED_OFF we shoulda moved this one with it */
+ 					if (nextTstatus == HEAPTUPLE_DELETE_IN_PROGRESS)
+ 						elog(ERROR, "updated tuple is already HEAP_MOVED_OFF");
  					/* OK, switch our attention to the next tuple in chain */
  					tp.t_data = nextTdata;
  					tp.t_self = nextTid;
***************
*** 2034,2039 ****
--- 2064,2074 ----
  					free_vtmove--;
  					num_vtmove++;
  
+ 					/* Remember if we reached the original target tuple */
+ 					if (ItemPointerGetBlockNumber(&tp.t_self) == blkno &&
+ 						ItemPointerGetOffsetNumber(&tp.t_self) == offnum)
+ 						moved_target = true;
+ 
  					/* Done if at beginning of chain */
  					if (!(tp.t_data->t_infomask & HEAP_UPDATED) ||
  					 TransactionIdPrecedes(HeapTupleHeaderGetXmin(tp.t_data),
***************
*** 2102,2107 ****
--- 2137,2149 ----
  					ReleaseBuffer(Cbuf);
  				freeCbuf = false;
  
+ 				/* Double-check that we will move the current target tuple */
+ 				if (!moved_target && !chain_move_failed)
+ 				{
+ 					elog(DEBUG2, "failed to chain back to target --- cannot continue repair_frag");
+ 					chain_move_failed = true;
+ 				}
+ 
  				if (chain_move_failed)
  				{
  					/*