rewritehandler.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

{
	/* Don't scribble on the passed qual (it's in the relcache!) */
	Node	   *new_qual = (Node *) copyObject(rule_qual);

	/*
	 * In case there are subqueries in the qual, acquire necessary locks and
	 * fix any deleted JOIN RTE entries.  (This is somewhat redundant with
	 * rewriteRuleAction, but not entirely ... consider restructuring so that
	 * we only need to process the qual this way once.)
	 */
	(void) acquireLocksOnSubLinks(new_qual, NULL);

	/* Fix references to OLD */
	ChangeVarNodes(new_qual, PRS2_OLD_VARNO, rt_index, 0);
	/* Fix references to NEW */
	if (event == CMD_INSERT || event == CMD_UPDATE)
		new_qual = ResolveNew(new_qual,
							  PRS2_NEW_VARNO,
							  0,
							  rt_fetch(rt_index, parsetree->rtable),
							  parsetree->targetList,
							  event,
							  rt_index);
	/* And attach the fixed qual */
	AddInvertedQual(parsetree, new_qual);

	return parsetree;
}


/*
 *	fireRules -
 *	   Iterate through rule locks applying rules.
 *
 * Input arguments:
 *	parsetree - original query
 *	rt_index - RT index of result relation in original query
 *	event - type of rule event
 *	locks - list of rules to fire
 * Output arguments:
 *	*instead_flag - set TRUE if any unqualified INSTEAD rule is found
 *					(must be initialized to FALSE)
 *	*qual_product - filled with modified original query if any qualified
 *					INSTEAD rule is found (must be initialized to NULL)
 * Return value:
 *	list of rule actions adjusted for use with this query
 *
 * Qualified INSTEAD rules generate their action with the qualification
 * condition added.  They also generate a modified version of the original
 * query with the negated qualification added, so that it will run only for
 * rows that the qualified action doesn't act on.  (If there are multiple
 * qualified INSTEAD rules, we AND all the negated quals onto a single
 * modified original query.)  We won't execute the original, unmodified
 * query if we find either qualified or unqualified INSTEAD rules.	If
 * we find both, the modified original query is discarded too.
 */
static List *
fireRules(Query *parsetree,
		  int rt_index,
		  CmdType event,
		  List *locks,
		  bool *instead_flag,
		  Query **qual_product)
{
	List	   *results = NIL;
	ListCell   *l;

	foreach(l, locks)
	{
		RewriteRule *rule_lock = (RewriteRule *) lfirst(l);
		Node	   *event_qual = rule_lock->qual;
		List	   *actions = rule_lock->actions;
		QuerySource qsrc;
		ListCell   *r;

		/* Determine correct QuerySource value for actions */
		if (rule_lock->isInstead)
		{
			if (event_qual != NULL)
				qsrc = QSRC_QUAL_INSTEAD_RULE;
			else
			{
				qsrc = QSRC_INSTEAD_RULE;
				*instead_flag = true;	/* report unqualified INSTEAD */
			}
		}
		else
			qsrc = QSRC_NON_INSTEAD_RULE;

		if (qsrc == QSRC_QUAL_INSTEAD_RULE)
		{
			/*
			 * If there are INSTEAD rules with qualifications, the original
			 * query is still performed. But all the negated rule
			 * qualifications of the INSTEAD rules are added so it does its
			 * actions only in cases where the rule quals of all INSTEAD rules
			 * are false. Think of it as the default action in a case. We save
			 * this in *qual_product so RewriteQuery() can add it to the query
			 * list after we mangled it up enough.
			 *
			 * If we have already found an unqualified INSTEAD rule, then
			 * *qual_product won't be used, so don't bother building it.
			 */
			if (!*instead_flag)
			{
				if (*qual_product == NULL)
					*qual_product = copyObject(parsetree);
				*qual_product = CopyAndAddInvertedQual(*qual_product,
													   event_qual,
													   rt_index,
													   event);
			}
		}

		/* Now process the rule's actions and add them to the result list */
		foreach(r, actions)
		{
			Query	   *rule_action = lfirst(r);

			if (rule_action->commandType == CMD_NOTHING)
				continue;

			rule_action = rewriteRuleAction(parsetree, rule_action,
											event_qual, rt_index, event);

			rule_action->querySource = qsrc;
			rule_action->canSetTag = false;		/* might change later */

			results = lappend(results, rule_action);
		}
	}

	return results;
}


/*
 * RewriteQuery -
 *	  rewrites the query and apply the rules again on the queries rewritten
 *
 * rewrite_events is a list of open query-rewrite actions, so we can detect
 * infinite recursion.
 */
static List *
RewriteQuery(Query *parsetree, List *rewrite_events)
{
	CmdType		event = parsetree->commandType;
	bool		instead = false;
	Query	   *qual_product = NULL;
	List	   *rewritten = NIL;

	/*
	 * If the statement is an update, insert or delete - fire rules on it.
	 *
	 * SELECT rules are handled later when we have all the queries that should
	 * get executed.  Also, utilities aren't rewritten at all (do we still
	 * need that check?)
	 */
	if (event != CMD_SELECT && event != CMD_UTILITY)
	{
		int			result_relation;
		RangeTblEntry *rt_entry;
		Relation	rt_entry_relation;
		List	   *locks;

		result_relation = parsetree->resultRelation;
		Assert(result_relation != 0);
		rt_entry = rt_fetch(result_relation, parsetree->rtable);
		Assert(rt_entry->rtekind == RTE_RELATION);

		/*
		 * We can use NoLock here since either the parser or
		 * AcquireRewriteLocks should have locked the rel already.
		 */
		rt_entry_relation = heap_open(rt_entry->relid, NoLock);

		/*
		 * If it's an INSERT or UPDATE, rewrite the targetlist into standard
		 * form.  This will be needed by the planner anyway, and doing it now
		 * ensures that any references to NEW.field will behave sanely.
		 */
		if (event == CMD_INSERT || event == CMD_UPDATE)
			rewriteTargetList(parsetree, rt_entry_relation);

		/*
		 * Collect and apply the appropriate rules.
		 */
		locks = matchLocks(event, rt_entry_relation->rd_rules,
						   result_relation, parsetree);

		if (locks != NIL)
		{
			List	   *product_queries;

			product_queries = fireRules(parsetree,
										result_relation,
										event,
										locks,
										&instead,
										&qual_product);

			/*
			 * If we got any product queries, recursively rewrite them --- but
			 * first check for recursion!
			 */
			if (product_queries != NIL)
			{
				ListCell   *n;
				rewrite_event *rev;

				foreach(n, rewrite_events)
				{
					rev = (rewrite_event *) lfirst(n);
					if (rev->relation == RelationGetRelid(rt_entry_relation) &&
						rev->event == event)
						ereport(ERROR,
								(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
								 errmsg("infinite recursion detected in rules for relation \"%s\"",
							   RelationGetRelationName(rt_entry_relation))));
				}

				rev = (rewrite_event *) palloc(sizeof(rewrite_event));
				rev->relation = RelationGetRelid(rt_entry_relation);
				rev->event = event;
				rewrite_events = lcons(rev, rewrite_events);

				foreach(n, product_queries)
				{
					Query	   *pt = (Query *) lfirst(n);
					List	   *newstuff;

					newstuff = RewriteQuery(pt, rewrite_events);
					rewritten = list_concat(rewritten, newstuff);
				}

				rewrite_events = list_delete_first(rewrite_events);
			}
		}

		heap_close(rt_entry_relation, NoLock);
	}

	/*
	 * For INSERTs, the original query is done first; for UPDATE/DELETE, it is
	 * done last.  This is needed because update and delete rule actions might
	 * not do anything if they are invoked after the update or delete is
	 * performed. The command counter increment between the query executions
	 * makes the deleted (and maybe the updated) tuples disappear so the scans
	 * for them in the rule actions cannot find them.
	 *
	 * If we found any unqualified INSTEAD, the original query is not done at
	 * all, in any form.  Otherwise, we add the modified form if qualified
	 * INSTEADs were found, else the unmodified form.
	 */
	if (!instead)
	{
		if (parsetree->commandType == CMD_INSERT)
		{
			if (qual_product != NULL)
				rewritten = lcons(qual_product, rewritten);
			else
				rewritten = lcons(parsetree, rewritten);
		}
		else
		{
			if (qual_product != NULL)
				rewritten = lappend(rewritten, qual_product);
			else
				rewritten = lappend(rewritten, parsetree);
		}
	}

	return rewritten;
}


/*
 * QueryRewrite -
 *	  Primary entry point to the query rewriter.
 *	  Rewrite one query via query rewrite system, possibly returning 0
 *	  or many queries.
 *
 * NOTE: the parsetree must either have come straight from the parser,
 * or have been scanned by AcquireRewriteLocks to acquire suitable locks.
 */
List *
QueryRewrite(Query *parsetree)
{
	List	   *querylist;
	List	   *results = NIL;
	ListCell   *l;
	CmdType		origCmdType;
	bool		foundOriginalQuery;
	Query	   *lastInstead;

	/*
	 * Step 1
	 *
	 * Apply all non-SELECT rules possibly getting 0 or many queries
	 */
	querylist = RewriteQuery(parsetree, NIL);

	/*
	 * Step 2
	 *
	 * Apply all the RIR rules on each query
	 */
	foreach(l, querylist)
	{
		Query	   *query = (Query *) lfirst(l);

		query = fireRIRrules(query, NIL);

		/*
		 * If the query target was rewritten as a view, complain.
		 */
		if (query->resultRelation)
		{
			RangeTblEntry *rte = rt_fetch(query->resultRelation,
										  query->rtable);

			if (rte->rtekind == RTE_SUBQUERY)
			{
				switch (query->commandType)
				{
					case CMD_INSERT:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot insert into a view"),
								 errhint("You need an unconditional ON INSERT DO INSTEAD rule.")));
						break;
					case CMD_UPDATE:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot update a view"),
								 errhint("You need an unconditional ON UPDATE DO INSTEAD rule.")));
						break;
					case CMD_DELETE:
						ereport(ERROR,
								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
								 errmsg("cannot delete from a view"),
								 errhint("You need an unconditional ON DELETE DO INSTEAD rule.")));
						break;
					default:
						elog(ERROR, "unrecognized commandType: %d",
							 (int) query->commandType);
						break;
				}
			}
		}

		results = lappend(results, query);
	}

	/*
	 * Step 3
	 *
	 * Determine which, if any, of the resulting queries is supposed to set
	 * the command-result tag; and update the canSetTag fields accordingly.
	 *
	 * If the original query is still in the list, it sets the command tag.
	 * Otherwise, the last INSTEAD query of the same kind as the original is
	 * allowed to set the tag.	(Note these rules can leave us with no query
	 * setting the tag.  The tcop code has to cope with this by setting up a
	 * default tag based on the original un-rewritten query.)
	 *
	 * The Asserts verify that at most one query in the result list is marked
	 * canSetTag.  If we aren't checking asserts, we can fall out of the loop
	 * as soon as we find the original query.
	 */
	origCmdType = parsetree->commandType;
	foundOriginalQuery = false;
	lastInstead = NULL;

	foreach(l, results)
	{
		Query	   *query = (Query *) lfirst(l);

		if (query->querySource == QSRC_ORIGINAL)
		{
			Assert(query->canSetTag);
			Assert(!foundOriginalQuery);
			foundOriginalQuery = true;
#ifndef USE_ASSERT_CHECKING
			break;
#endif
		}
		else
		{
			Assert(!query->canSetTag);
			if (query->commandType == origCmdType &&
				(query->querySource == QSRC_INSTEAD_RULE ||
				 query->querySource == QSRC_QUAL_INSTEAD_RULE))
				lastInstead = query;
		}
	}

	if (!foundOriginalQuery && lastInstead != NULL)
		lastInstead->canSetTag = true;

	return results;
}