Function initNextTableToScan

src/backend/executor/nodeDynamicForeignscan.c:125–188

* initNextTableToScan * Find the next table to scan and initiate the scan if the previous table * is finished. * * If scanning on the current table is not finished, or a new table is found, * this function returns true. * If no more tables are found, this function returns false. */

 * If no more tables are found, this function returns false.
 */
static bool
initNextTableToScan(DynamicForeignScanState *node)
{
	ScanState  *scanState = (ScanState *) node;
	DynamicForeignScan *plan = (DynamicForeignScan *) scanState->ps.plan;
	EState	   *estate = scanState->ps.state;
	Relation	lastScannedRel;
	TupleDesc	partTupDesc;
	TupleDesc	lastTupDesc;
	AttrMap *attMap;
	Oid		   *pid;
	Relation	currentRelation;

	if (++node->whichPart < node->nOids)
		pid = &node->partOids[node->whichPart];
	else
		return false;

	/* Collect number of partitions scanned in EXPLAIN ANALYZE */
	if (NULL != scanState->ps.instrument)
	{
		Instrumentation *instr = scanState->ps.instrument;
		instr->numPartScanned++;
	}

	currentRelation = scanState->ss_currentRelation =
		table_open(node->partOids[node->whichPart], AccessShareLock);

	if (currentRelation->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
	{
		/* shouldn't happen */
		elog(ERROR, "unexpected relkind in Dynamic Foreign Scan: %c", currentRelation->rd_rel->relkind);
	}
	lastScannedRel = table_open(node->lastRelOid, AccessShareLock);
	lastTupDesc = RelationGetDescr(lastScannedRel);
	partTupDesc = RelationGetDescr(scanState->ss_currentRelation);
	/*
	 * FIXME: should we use execute_attr_map_tuple instead? Seems like a
	 * higher level abstraction that fits the bill
	 */
	attMap = build_attrmap_by_name_if_req(partTupDesc, lastTupDesc);
	table_close(lastScannedRel, AccessShareLock);

	/* If attribute remapping is not necessary, then do not change the varattno */
	if (attMap)
	{
		change_varattnos_of_a_varno((Node*)scanState->ps.plan->qual, attMap->attnums, node->scanrelid);
		change_varattnos_of_a_varno((Node*)scanState->ps.plan->targetlist, attMap->attnums, node->scanrelid);

		/*
		 * Now that the varattno mapping has been changed, change the relation that
		 * the new varnos correspond to
		 */
		node->lastRelOid = *pid;
		free_attrmap(attMap);
	}

	RangeTblEntry *rte = exec_rt_fetch(node->scanrelid, estate);