diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 21f5e2c..639bd71 100644
*** a/src/backend/postmaster/autovacuum.c
--- b/src/backend/postmaster/autovacuum.c
*************** typedef struct autovac_table
*** 212,220 ****
   * wi_launchtime Time at which this worker was launched
   * wi_cost_*	Vacuum cost-based delay parameters current in this worker
   *
!  * All fields are protected by AutovacuumLock, except for wi_tableoid which is
!  * protected by AutovacuumScheduleLock (which is read-only for everyone except
!  * that worker itself).
   *-------------
   */
  typedef struct WorkerInfoData
--- 212,220 ----
   * wi_launchtime Time at which this worker was launched
   * wi_cost_*	Vacuum cost-based delay parameters current in this worker
   *
!  * All fields are protected by AutovacuumLock, except for wi_tableoid and
!  * wi_sharedrel which are protected by AutovacuumScheduleLock (note these
!  * two fields are read-only for everyone except that worker itself).
   *-------------
   */
  typedef struct WorkerInfoData
*************** do_autovacuum(void)
*** 2317,2323 ****
--- 2317,2325 ----
  	foreach(cell, table_oids)
  	{
  		Oid			relid = lfirst_oid(cell);
+ 		HeapTuple	classTup;
  		autovac_table *tab;
+ 		bool		isshared;
  		bool		skipit;
  		int			stdVacuumCostDelay;
  		int			stdVacuumCostLimit;
*************** do_autovacuum(void)
*** 2342,2350 ****
  		}
  
  		/*
! 		 * hold schedule lock from here until we're sure that this table still
! 		 * needs vacuuming.  We also need the AutovacuumLock to walk the
! 		 * worker array, but we'll let go of that one quickly.
  		 */
  		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
  		LWLockAcquire(AutovacuumLock, LW_SHARED);
--- 2344,2366 ----
  		}
  
  		/*
! 		 * Find out whether the table is shared or not.  (It's slightly
! 		 * annoying to fetch the syscache entry just for this, but in typical
! 		 * cases it adds little cost because table_recheck_autovac would
! 		 * refetch the entry anyway.  We could buy that back by copying the
! 		 * tuple here and passing it to table_recheck_autovac, but that
! 		 * increases the odds of that function working with stale data.)
! 		 */
! 		classTup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
! 		if (!HeapTupleIsValid(classTup))
! 			continue;			/* somebody deleted the rel, forget it */
! 		isshared = ((Form_pg_class) GETSTRUCT(classTup))->relisshared;
! 		ReleaseSysCache(classTup);
! 
! 		/*
! 		 * Hold schedule lock from here until we've claimed the table.  We
! 		 * also need the AutovacuumLock to walk the worker array, but that one
! 		 * can just be a shared lock.
  		 */
  		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
  		LWLockAcquire(AutovacuumLock, LW_SHARED);
*************** do_autovacuum(void)
*** 2381,2386 ****
--- 2397,2412 ----
  		}
  
  		/*
+ 		 * Store the table's OID in shared memory before releasing the
+ 		 * schedule lock, so that other workers don't try to vacuum it
+ 		 * concurrently.  (We claim it here so as not to hold
+ 		 * AutovacuumScheduleLock while rechecking the stats.)
+ 		 */
+ 		MyWorkerInfo->wi_tableoid = relid;
+ 		MyWorkerInfo->wi_sharedrel = isshared;
+ 		LWLockRelease(AutovacuumScheduleLock);
+ 
+ 		/*
  		 * Check whether pgstat data still says we need to vacuum this table.
  		 * It could have changed if something else processed the table while
  		 * we weren't looking.
*************** do_autovacuum(void)
*** 2396,2414 ****
  		if (tab == NULL)
  		{
  			/* someone else vacuumed the table, or it went away */
  			LWLockRelease(AutovacuumScheduleLock);
  			continue;
  		}
  
  		/*
- 		 * Ok, good to go.  Store the table in shared memory before releasing
- 		 * the lock so that other workers don't vacuum it concurrently.
- 		 */
- 		MyWorkerInfo->wi_tableoid = relid;
- 		MyWorkerInfo->wi_sharedrel = tab->at_sharedrel;
- 		LWLockRelease(AutovacuumScheduleLock);
- 
- 		/*
  		 * Remember the prevailing values of the vacuum cost GUCs.  We have to
  		 * restore these at the bottom of the loop, else we'll compute wrong
  		 * values in the next iteration of autovac_balance_cost().
--- 2422,2435 ----
  		if (tab == NULL)
  		{
  			/* someone else vacuumed the table, or it went away */
+ 			LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
+ 			MyWorkerInfo->wi_tableoid = InvalidOid;
+ 			MyWorkerInfo->wi_sharedrel = false;
  			LWLockRelease(AutovacuumScheduleLock);
  			continue;
  		}
  
  		/*
  		 * Remember the prevailing values of the vacuum cost GUCs.  We have to
  		 * restore these at the bottom of the loop, else we'll compute wrong
  		 * values in the next iteration of autovac_balance_cost().
*************** deleted:
*** 2522,2531 ****
  		 * settings, so we don't want to give up our share of I/O for a very
  		 * short interval and thereby thrash the global balance.
  		 */
! 		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
  		MyWorkerInfo->wi_tableoid = InvalidOid;
  		MyWorkerInfo->wi_sharedrel = false;
! 		LWLockRelease(AutovacuumLock);
  
  		/* restore vacuum cost GUCs for the next iteration */
  		VacuumCostDelay = stdVacuumCostDelay;
--- 2543,2552 ----
  		 * settings, so we don't want to give up our share of I/O for a very
  		 * short interval and thereby thrash the global balance.
  		 */
! 		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
  		MyWorkerInfo->wi_tableoid = InvalidOid;
  		MyWorkerInfo->wi_sharedrel = false;
! 		LWLockRelease(AutovacuumScheduleLock);
  
  		/* restore vacuum cost GUCs for the next iteration */
  		VacuumCostDelay = stdVacuumCostDelay;