Function tablesample_getnext

src/backend/executor/nodeSamplescan.c:334–378

* Get next tuple from TABLESAMPLE method. */

 * Get next tuple from TABLESAMPLE method.
 */
static TupleTableSlot *
tablesample_getnext(SampleScanState *scanstate)
{
	TableScanDesc scan = scanstate->ss.ss_currentScanDesc;
	TupleTableSlot *slot = scanstate->ss.ss_ScanTupleSlot;

	ExecClearTuple(slot);

	if (scanstate->done)
		return NULL;

	for (;;)
	{
		if (!scanstate->haveblock)
		{
			if (!table_scan_sample_next_block(scan, scanstate))
			{
				scanstate->haveblock = false;
				scanstate->done = true;

				/* exhausted relation */
				return NULL;
			}

			scanstate->haveblock = true;
		}

		if (!table_scan_sample_next_tuple(scan, scanstate, slot))
		{
			/*
			 * If we get here, it means we've exhausted the items on this page
			 * and it's time to move to the next.
			 */
			scanstate->haveblock = false;
			continue;
		}

		/* Found visible tuple, return it. */
		break;
	}

	scanstate->donetuples++;

	return slot;
}