Function BitmapHeapNext

src/backend/executor/nodeBitmapHeapscan.c:113–392

---------------------------------------------------------------- * BitmapHeapNext * * Retrieve next tuple from the BitmapHeapScan node's currentRelation * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static TupleTableSlot *
BitmapHeapNext(BitmapHeapScanState *node)
{
	ExprContext *econtext;
	TableScanDesc scan;
	Node  		*tbm;
	GenericBMIterator *tbmiterator = NULL;
	TBMIterateResult *tbmres;
#ifdef USE_PREFETCH
	GenericBMIterator *prefetch_iterator;
#endif

	TBMSharedIterator *shared_tbmiterator = NULL;
	TupleTableSlot *slot;
	ParallelBitmapHeapState *pstate = node->pstate;
	dsa_area   *dsa = node->ss.ps.state->es_query_dsa;

	/*
	 * extract necessary information from index scan node
	 */
	econtext = node->ss.ps.ps_ExprContext;
	slot = node->ss.ss_ScanTupleSlot;
	scan = node->ss.ss_currentScanDesc;
	tbm = node->tbm;
	if (pstate == NULL)
		tbmiterator = node->tbmiterator;
	else
		shared_tbmiterator = node->shared_tbmiterator;
	tbmres = node->tbmres;

	/*
	 * If we haven't yet performed the underlying index scan, do it, and begin
	 * the iteration over the bitmap.
	 *
	 * For prefetching, we use *two* iterators, one for the pages we are
	 * actually scanning and another that runs ahead of the first for
	 * prefetching.  node->prefetch_pages tracks exactly how many pages ahead
	 * the prefetch iterator is.  Also, node->prefetch_target tracks the
	 * desired prefetch distance, which starts small and increases up to the
	 * node->prefetch_maximum.  This is to avoid doing a lot of prefetching in
	 * a scan that stops after a few tuples because of a LIMIT.
	 */
	if (!node->initialized)
	{
		if (!pstate)
		{
			tbm = (Node *) MultiExecProcNode(outerPlanState(node));

			if (!tbm || !(IsA(tbm, TIDBitmap) || IsA(tbm, StreamBitmap)))
				elog(ERROR, "unrecognized result from subplan");

			node->tbm = tbm;
			node->tbmiterator = tbmiterator = tbm_generic_begin_iterate(tbm);
			node->tbmres = tbmres = NULL;

#ifdef USE_PREFETCH
			if (node->prefetch_maximum > 0)
			{