Function ExecReScanHashJoin

src/backend/executor/nodeHashjoin.c:1668–1768

void
ExecReScanHashJoin(HashJoinState *node)
{
	/*
	 * In a multi-batch join, we currently have to do rescans the hard way,
	 * primarily because batch temp files may have already been released. But
	 * if it's a single-batch join, and there is no parameter change for the
	 * inner subnode, then we can just re-use the existing hash table without
	 * rebuilding it.
	 */
	if (node->hj_HashTable != NULL)
	{
		node->hj_HashTable->first_pass = false;

		if (node->js.ps.righttree->chgParam == NULL &&
			!node->hj_HashTable->eagerlyReleased)
		{
			/*
			 * Okay to reuse the hash table; needn't rescan inner, either.
			 *
			 * However, if it's a right/full join, we'd better reset the
			 * inner-tuple match flags contained in the table.
			 */
			if (HJ_FILL_INNER(node))
				ExecHashTableResetMatchFlags(node->hj_HashTable);

			/*
			 * Also, we need to reset our state about the emptiness of the
			 * outer relation, so that the new scan of the outer will update
			 * it correctly if it turns out to be empty this time. (There's no
			 * harm in clearing it now because ExecHashJoin won't need the
			 * info.  In the other cases, where the hash table doesn't exist
			 * or we are destroying it, we leave this state alone because
			 * ExecHashJoin will need it the first time through.)
			 */
			node->hj_OuterNotEmpty = false;

			/* ExecHashJoin can skip the BUILD_HASHTABLE step */
			node->hj_JoinState = HJ_NEED_NEW_OUTER;

			if (node->hj_HashTable->nbatch > 1)
			{
				/* Force reloading batch 0 upon next ExecHashJoin */
				node->hj_HashTable->curbatch = -1;
			}
			else
			{
				/* MPP-1600: reset the batch number */
				node->hj_HashTable->curbatch = 0;
			}
		}
		else
		{
			/* must destroy and rebuild hash table */
			if (!node->hj_HashTable->eagerlyReleased)
			{
				HashState  *hashNode = castNode(HashState, innerPlanState(node));