*** a/src/backend/commands/vacuumlazy.c
--- b/src/backend/commands/vacuumlazy.c
***************
*** 96,101 ****
--- 96,108 ----
   */
  #define SKIP_PAGES_THRESHOLD	((BlockNumber) 32)
  
+ /*
+  * The following two values are used for identifying whether any table contains
+  * large number of unused rows and are eligible for 'VACUUM FULL'.
+  */
+ #define RELPAGES_VALUES_THRESHOLD 1000
+ #define FREESPACE_PERCENTAGE_THRESHOLD 0.5
+ 
  typedef struct LVRelStats
  {
  	/* hasindex = true means two-pass strategy; false means one-pass */
***************
*** 155,161 **** static bool lazy_tid_reaped(ItemPointer itemptr, void *state);
  static int	vac_cmp_itemptr(const void *left, const void *right);
  static bool heap_page_is_all_visible(Relation rel, Buffer buf,
  						 TransactionId *visibility_cutoff_xid);
! 
  
  /*
   *	lazy_vacuum_rel() -- perform LAZY VACUUM for one heap relation
--- 162,168 ----
  static int	vac_cmp_itemptr(const void *left, const void *right);
  static bool heap_page_is_all_visible(Relation rel, Buffer buf,
  						 TransactionId *visibility_cutoff_xid);
! static bool check_needs_full_vacuum(Relation rel, LVRelStats *vacrelstats);
  
  /*
   *	lazy_vacuum_rel() -- perform LAZY VACUUM for one heap relation
***************
*** 364,369 **** lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
--- 371,412 ----
  							pg_rusage_show(&ru0))));
  		}
  	}
+ 
+ 	if (check_needs_full_vacuum(onerel, vacrelstats))
+ 		ereport(LOG,
+ 				(errmsg("Table \"%s\" contains large numbers of unused row, suggest using VACUUM FULL on it!",
+ 						RelationGetRelationName(onerel))));
+ }
+ 
+ /*
+  * According the percentage of the free space in the table to check
+  * whether a table contains large numbers of unused row and are eligible for
+  * 'VACUUM FULL'
+  *
+  * Return: true -- need VACUUM FULL the table
+  */
+ static bool
+ check_needs_full_vacuum(Relation rel, LVRelStats *vacrelstats)
+ {
+ 	bool		ret = false;
+ 	BlockNumber i = 0;
+ 	Size		total_freespace = 0;
+ 
+ 	if (vacrelstats == NULL)
+ 		return false;
+ 
+ 	if (vacrelstats->rel_pages > RELPAGES_VALUES_THRESHOLD)
+ 	{
+ 		for (i = 0; i < vacrelstats->rel_pages; i++)
+ 		{
+ 			total_freespace += GetRecordedFreeSpace(rel, i);
+ 		}
+ 
+ 		if (total_freespace > vacrelstats->rel_pages * BLCKSZ * FREESPACE_PERCENTAGE_THRESHOLD)
+ 			ret = true;
+ 	}
+ 
+ 	return ret;
  }
  
  /*