Fix some problems with VACUUM (INDEX_CLEANUP FALSE).

The new nleft_dead_tuples and nleft_dead_itemids fields are confusing
and do not seem like the correct way forward.  One of them is tested
via an assertion that can fail, as it has already done on buildfarm
member topminnow.  Remove the assertion and the fields.

Change the logic for the case where a tuple is not initially pruned
by heap_page_prune but later diagnosed HEAPTUPLE_DEAD by
HeapTupleSatisfiesVacuum.  Previously, tupgone = true was set in
that case, which leads to treating the tuple as one that will be
removed.  In a normal vacuum, that's OK, because we'll remove
index entries for it and then the second heap pass will remove the
tuple itself, but when index cleanup is disabled, those things
don't happen, so we must instead treat it as a recently-dead
tuple that we have voluntarily chosen to keep.

Report and analysis by Tom Lane.  This patch loosely based on one
from Masahiko Sawada, but I changed most of it.

Author: robertmhaas

src/backend/access/heap/vacuumlazy.c

@@ -125,8 +125,6 @@ typedef struct LVRelStats
 	double		new_rel_tuples; /* new estimated total # of tuples */
 	double		new_live_tuples;	/* new estimated total # of live tuples */
 	double		new_dead_tuples;	/* new estimated total # of dead tuples */
-	double		nleft_dead_tuples;	/* # of dead tuples we left */
-	double		nleft_dead_itemids;	/* # of dead item pointers we left */
 	BlockNumber pages_removed;
 	double		tuples_deleted;
 	BlockNumber nonempty_pages; /* actually, last nonempty page + 1 */
@@ -427,12 +425,6 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 							 vacrelstats->new_rel_tuples,
 							 vacrelstats->new_dead_tuples,
 							 OldestXmin);
-			if (vacrelstats->nleft_dead_tuples > 0 ||
-				vacrelstats->nleft_dead_itemids > 0)
-				appendStringInfo(&buf,
-								 _("%.0f tuples and %.0f item identifiers are left as dead.\n"),
-								 vacrelstats->nleft_dead_tuples,
-								 vacrelstats->nleft_dead_itemids);
 			appendStringInfo(&buf,
 							 _("buffer usage: %d hits, %d misses, %d dirtied\n"),
 							 VacuumPageHit,
@@ -515,10 +507,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 				live_tuples,	/* live tuples (reltuples estimate) */
 				tups_vacuumed,	/* tuples cleaned up by vacuum */
 				nkeep,			/* dead-but-not-removable tuples */
-				nunused,		/* unused item pointers */
-				nleft_dead_tuples,		/* tuples we left as dead */
-				nleft_dead_itemids;		/* item pointers we left as dead,
-										 * includes nleft_dead_tuples. */
+				nunused;		/* unused item pointers */
 	IndexBulkDeleteResult **indstats;
 	int			i;
 	PGRUsage	ru0;
@@ -551,7 +540,6 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 	empty_pages = vacuumed_pages = 0;
 	next_fsm_block_to_vacuum = (BlockNumber) 0;
 	num_tuples = live_tuples = tups_vacuumed = nkeep = nunused = 0;
-	nleft_dead_itemids = nleft_dead_tuples = 0;
 
 	indstats = (IndexBulkDeleteResult **)
 		palloc0(nindexes * sizeof(IndexBulkDeleteResult *));
@@ -1075,7 +1063,11 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 					 * it were RECENTLY_DEAD.  Also, if it's a heap-only
 					 * tuple, we choose to keep it, because it'll be a lot
 					 * cheaper to get rid of it in the next pruning pass than
-					 * to treat it like an indexed tuple.
+					 * to treat it like an indexed tuple. Finally, if index
+					 * cleanup is disabled, the second heap pass will not
+					 * execute, and the tuple will not get removed, so we
+					 * must treat it like any other dead tuple that we choose
+					 * to keep.
 					 *
 					 * If this were to happen for a tuple that actually needed
 					 * to be deleted, we'd be in trouble, because it'd
@@ -1085,20 +1077,11 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 					 * preventing corruption.
 					 */
 					if (HeapTupleIsHotUpdated(&tuple) ||
-						HeapTupleIsHeapOnly(&tuple))
+						HeapTupleIsHeapOnly(&tuple) ||
+						params->index_cleanup == VACOPT_TERNARY_DISABLED)
 						nkeep += 1;
 					else
-					{
 						tupgone = true; /* we can delete the tuple */
-
-						/*
-						 * Since this dead tuple will not be vacuumed and
-						 * ignored when index cleanup is disabled we count
-						 * count it for reporting.
-						 */
-						if (params->index_cleanup == VACOPT_TERNARY_ENABLED)
-							nleft_dead_tuples++;
-					}
 					all_visible = false;
 					break;
 				case HEAPTUPLE_LIVE:
@@ -1275,7 +1258,6 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 				 * the next vacuum will process them anyway.
 				 */
 				Assert(params->index_cleanup == VACOPT_TERNARY_DISABLED);
-				nleft_dead_itemids += vacrelstats->num_dead_tuples;
 			}
 
 			/*
@@ -1402,21 +1384,14 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 			RecordPageWithFreeSpace(onerel, blkno, freespace, nblocks);
 	}
 
-	/* No dead tuples should be left if index cleanup is enabled */
-	Assert((params->index_cleanup == VACOPT_TERNARY_ENABLED &&
-			nleft_dead_tuples == 0 && nleft_dead_itemids == 0) ||
-		   params->index_cleanup == VACOPT_TERNARY_DISABLED);
-
 	/* report that everything is scanned and vacuumed */
 	pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
 
 	pfree(frozen);
 
 	/* save stats for use later */
 	vacrelstats->tuples_deleted = tups_vacuumed;
-	vacrelstats->new_dead_tuples = nkeep + nleft_dead_tuples;
-	vacrelstats->nleft_dead_tuples = nleft_dead_tuples;
-	vacrelstats->nleft_dead_itemids = nleft_dead_itemids;
+	vacrelstats->new_dead_tuples = nkeep;
 
 	/* now we can compute the new value for pg_class.reltuples */
 	vacrelstats->new_live_tuples = vac_estimate_reltuples(onerel,
@@ -1520,8 +1495,6 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 									"%u pages are entirely empty.\n",
 									empty_pages),
 					 empty_pages);
-	appendStringInfo(&buf, "%.0f tuples and %.0f item identifiers are left as dead.\n",
-					 nleft_dead_tuples, nleft_dead_itemids);
 	appendStringInfo(&buf, _("%s."), pg_rusage_show(&ru0));
 
 	ereport(elevel,