diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
new file mode 100644
index 76b3a46..472b780
*** a/src/backend/access/heap/visibilitymap.c
--- b/src/backend/access/heap/visibilitymap.c
***************
*** 88,93 ****
--- 88,94 ----
  #include "storage/bufmgr.h"
  #include "storage/lmgr.h"
  #include "storage/smgr.h"
+ #include "utils/inval.h"
  
  
  /*#define TRACE_VISIBILITYMAP */
*************** vm_readbuf(Relation rel, BlockNumber blk
*** 486,497 ****
  
  	/*
  	 * If we haven't cached the size of the visibility map fork yet, check it
! 	 * first.  Also recheck if the requested block seems to be past end, since
! 	 * our cached value might be stale.  (We send smgr inval messages on
! 	 * truncation, but not on extension.)
  	 */
! 	if (rel->rd_smgr->smgr_vm_nblocks == InvalidBlockNumber ||
! 		blkno >= rel->rd_smgr->smgr_vm_nblocks)
  	{
  		if (smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
  			rel->rd_smgr->smgr_vm_nblocks = smgrnblocks(rel->rd_smgr,
--- 487,497 ----
  
  	/*
  	 * If we haven't cached the size of the visibility map fork yet, check it
! 	 * first.  This will also catch any changes to the visibility map's size
! 	 * made by other backends, since we send smgr inval messages on create,
! 	 * extend and truncate.
  	 */
! 	if (rel->rd_smgr->smgr_vm_nblocks == InvalidBlockNumber)
  	{
  		if (smgrexists(rel->rd_smgr, VISIBILITYMAP_FORKNUM))
  			rel->rd_smgr->smgr_vm_nblocks = smgrnblocks(rel->rd_smgr,
*************** vm_extend(Relation rel, BlockNumber vm_n
*** 560,565 ****
--- 560,575 ----
  
  	vm_nblocks_now = smgrnblocks(rel->rd_smgr, VISIBILITYMAP_FORKNUM);
  
+ 	/*
+ 	 * Send a shared-inval message to force other backends to close any smgr
+ 	 * references they may have for this rel, which we are about to change.
+ 	 * This is a useful optimization because it means that backends don't have
+ 	 * to keep checking for creation or extension of the file, which happens
+ 	 * infrequently.
+ 	 */
+ 	CacheInvalidateSmgr(rel->rd_smgr->smgr_rnode);
+ 
+ 	/* Now extend the file */
  	while (vm_nblocks_now < vm_nblocks)
  	{
  		smgrextend(rel->rd_smgr, VISIBILITYMAP_FORKNUM, vm_nblocks_now,