heap_page_prune_opt()
{
  minfree = RelationGetTargetPageFreeSpace();
  minfree = Max(minfree, BLCKSZ / 10);
  
  if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
  {
    if (!ConditionalLockBufferForCleanup(buffer))
      continue;
    if (PageIsFull(page) || PageGetHeapFreeSpace(page) < minfree)
    {
      heap_page_prune();
    }
  }
}

heap_page_prune()
{
  for (offnum = FirstOffsetNumber;
       offnum <= maxoff;
       offnum = OffsetNumberNext(offnum))
  {
    heap_prune_chain(&prstate)
  }
  
  if (prstate.nredirected > 0 || prstate.ndead > 0 || prstate.nunused > 0)
  {
    heap_page_prune_execute();
  }
     
}

heap_prune_chain()
{
  /* while not end of the chain */
  for (;;)
  {
    lp = PageGetItemId(dp, offnum);
    /* Unused item obviously isn't part of the chain */
    if (!ItemIdIsUsed(lp))
      break;
      
    if (ItemIdIsRedirected(lp))
    {
      if (nchain > 0)
        break;			/* not at start of chain */
      chainitems[nchain++] = offnum;
      offnum = ItemIdGetRedirect(rootlp);
      continue;
    }
    
    if (ItemIdIsDead(lp))
      break;
    
    htup = (HeapTupleHeader) PageGetItem(dp, lp);
    
    /*
     * Check the tuple XMIN against prior XMAX, if any
     */
    if (TransactionIdIsValid(priorXmax) &&
      !TransactionIdEquals(HeapTupleHeaderGetXmin(htup), priorXmax))
      break;

     /* record each item of this chain */
     chainitems[nchain++] = offnum;
    
    switch ((HTSV_Result) prstate->htsv[offnum])
    {
      case: HEAPTUPLE_DEAD:
        tupdead = true;
        break;
      case HEAPTUPLE_RECENTLY_DEAD:
        heap_prune_record_prunable(prstate,
                                    HeapTupleHeaderGetUpdateXid(htup));
      ...
    }
    
  }
  
  if (OffsetNumberIsValid(latestdead))
  {
    for (i = 1; (i < nchain) && (chainitems[i - 1] != latestdead); i++)
    {
      heap_prune_record_unused(prstate, chainitems[i]);
      ndeleted++;
    }
    
    if (i >= nchain) /* The whole chain is dead */
      heap_prune_record_dead(prstate, rootoffnum);
    else						/* Or just redirect */
      heap_prune_record_redirect(prstate, rootoffnum, chainitems[i]);
  }
}

void
heap_page_prune_execute()
{
  /* redirect */
  for (int i = 0; i < nredirected; i++)
  {
    ItemIdSetRedirect(fromlp, tooff);
  }
  
  /* dead */
  for (int i = 0; i < ndead; i++)
  {
    ItemIdSetDead(lp);
  }
  
  /* unused */
  for (int i = 0; i < nunused; i++)
  {
    ItemIdSetUnused(lp);
  }
  PageRepairFragmentation();
  page_verify_redirects();
}

bool
heap_hot_search_buffer()
{
  blkno = ItemPointerGetBlockNumber(tid);
  offnum = ItemPointerGetOffsetNumber(tid);
  for (;;)
  {
    lp = PageGetItemId(page, offnum);
    heapTuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
  }
}