*** a/doc/src/sgml/config.sgml
--- b/doc/src/sgml/config.sgml
***************
*** 4955,4961 **** COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
          This parameter can only be set in the <filename>postgresql.conf</>
          file or on the server command line.
          This setting can be overridden for individual tables by
!         changing storage parameters.
         </para>
        </listitem>
       </varlistentry>
--- 4955,4962 ----
          This parameter can only be set in the <filename>postgresql.conf</>
          file or on the server command line.
          This setting can be overridden for individual tables by
!         changing storage parameters. The user specified value is ignored if it
!         is the same limit as <xref linkend="guc-vacuum-cost-limit"> value.
         </para>
        </listitem>
       </varlistentry>
*** a/src/backend/postmaster/autovacuum.c
--- b/src/backend/postmaster/autovacuum.c
***************
*** 1776,1795 **** autovac_balance_cost(void)
  	if (vac_cost_limit <= 0 || vac_cost_delay <= 0)
  		return;
  
! 	/* caculate the total base cost limit of active workers */
  	cost_total = 0.0;
  	dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
  	{
  		WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
  
  		if (worker->wi_proc != NULL &&
! 			worker->wi_cost_limit_base > 0 && worker->wi_cost_delay > 0)
  			cost_total +=
  				(double) worker->wi_cost_limit_base / worker->wi_cost_delay;
  	}
- 	/* there are no cost limits -- nothing to do */
- 	if (cost_total <= 0)
- 		return;
  
  	/*
  	 * Adjust cost limit of each active worker to balance the total of cost
--- 1776,1794 ----
  	if (vac_cost_limit <= 0 || vac_cost_delay <= 0)
  		return;
  
! 	/* calculate the total base cost limit of active workers */
  	cost_total = 0.0;
  	dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
  	{
  		WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
  
  		if (worker->wi_proc != NULL &&
! 			worker->wi_cost_limit_base > 0 &&
! 			worker->wi_cost_delay > 0 &&
! 			worker->wi_cost_limit_base == vac_cost_limit)
  			cost_total +=
  				(double) worker->wi_cost_limit_base / worker->wi_cost_delay;
  	}
  
  	/*
  	 * Adjust cost limit of each active worker to balance the total of cost
***************
*** 1803,1820 **** autovac_balance_cost(void)
  		if (worker->wi_proc != NULL &&
  			worker->wi_cost_limit_base > 0 && worker->wi_cost_delay > 0)
  		{
! 			int			limit = (int)
! 			(cost_avail * worker->wi_cost_limit_base / cost_total);
  
! 			/*
! 			 * We put a lower bound of 1 on the cost_limit, to avoid division-
! 			 * by-zero in the vacuum code.	Also, in case of roundoff trouble
! 			 * in these calculations, let's be sure we don't ever set
! 			 * cost_limit to more than the base value.
! 			 */
! 			worker->wi_cost_limit = Max(Min(limit,
! 											worker->wi_cost_limit_base),
! 										1);
  
  			elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, cost_limit=%d, cost_limit_base=%d, cost_delay=%d)",
  				 worker->wi_proc->pid, worker->wi_dboid, worker->wi_tableoid,
--- 1802,1823 ----
  		if (worker->wi_proc != NULL &&
  			worker->wi_cost_limit_base > 0 && worker->wi_cost_delay > 0)
  		{
! 			if (worker->wi_cost_limit_base == vac_cost_limit &&
! 				cost_total > 0)
! 			{
! 				int			limit = (int)
! 				(cost_avail * worker->wi_cost_limit_base / cost_total);
  
! 				/*
! 				 * We put a lower bound of 1 on the cost_limit, to avoid
! 				 * division- by-zero in the vacuum code.  Also, in case of
! 				 * roundoff trouble in these calculations, let's be sure we
! 				 * don't ever set cost_limit to more than the base value.
! 				 */
! 				worker->wi_cost_limit = Max(Min(limit,
! 												worker->wi_cost_limit_base),
! 											1);
! 			}
  
  			elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, cost_limit=%d, cost_limit_base=%d, cost_delay=%d)",
  				 worker->wi_proc->pid, worker->wi_dboid, worker->wi_tableoid,