rewritehandler.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * rewriteHandler.c
 *		Primary module of query rewriter.
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteHandler.c,v 1.158.2.2 2005/11/23 17:21:22 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/prep.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_type.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"


/* We use a list of these to detect recursion in RewriteQuery */
typedef struct rewrite_event
{
	Oid			relation;		/* OID of relation having rules */
	CmdType		event;			/* type of rule being fired */
} rewrite_event;

static bool acquireLocksOnSubLinks(Node *node, void *context);
static Query *rewriteRuleAction(Query *parsetree,
				  Query *rule_action,
				  Node *rule_qual,
				  int rt_index,
				  CmdType event);
static List *adjustJoinTreeList(Query *parsetree, bool removert, int rt_index);
static void rewriteTargetList(Query *parsetree, Relation target_relation);
static TargetEntry *process_matched_tle(TargetEntry *src_tle,
					TargetEntry *prior_tle,
					const char *attrName);
static Node *get_assignment_input(Node *node);
static void markQueryForLocking(Query *qry, bool forUpdate, bool noWait,
					bool skipOldNew);
static List *matchLocks(CmdType event, RuleLock *rulelocks,
		   int varno, Query *parsetree);
static Query *fireRIRrules(Query *parsetree, List *activeRIRs);


/*
 * AcquireRewriteLocks -
 *	  Acquire suitable locks on all the relations mentioned in the Query.
 *	  These locks will ensure that the relation schemas don't change under us
 *	  while we are rewriting and planning the query.
 *
 * A secondary purpose of this routine is to fix up JOIN RTE references to
 * dropped columns (see details below).  Because the RTEs are modified in
 * place, it is generally appropriate for the caller of this routine to have
 * first done a copyObject() to make a writable copy of the querytree in the
 * current memory context.
 *
 * This processing can, and for efficiency's sake should, be skipped when the
 * querytree has just been built by the parser: parse analysis already got
 * all the same locks we'd get here, and the parser will have omitted dropped
 * columns from JOINs to begin with.  But we must do this whenever we are
 * dealing with a querytree produced earlier than the current command.
 *
 * About JOINs and dropped columns: although the parser never includes an
 * already-dropped column in a JOIN RTE's alias var list, it is possible for
 * such a list in a stored rule to include references to dropped columns.
 * (If the column is not explicitly referenced anywhere else in the query,
 * the dependency mechanism won't consider it used by the rule and so won't
 * prevent the column drop.)  To support get_rte_attribute_is_dropped(),
 * we replace join alias vars that reference dropped columns with NULL Const
 * nodes.
 *
 * (In PostgreSQL 8.0, we did not do this processing but instead had
 * get_rte_attribute_is_dropped() recurse to detect dropped columns in joins.
 * That approach had horrible performance unfortunately; in particular
 * construction of a nested join was O(N^2) in the nesting depth.)
 */
void
AcquireRewriteLocks(Query *parsetree)
{
	ListCell   *l;
	int			rt_index;

	/*
	 * First, process RTEs of the current query level.
	 */
	rt_index = 0;
	foreach(l, parsetree->rtable)
	{
		RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
		Relation	rel;
		LOCKMODE	lockmode;
		List	   *newaliasvars;
		Index		curinputvarno;
		RangeTblEntry *curinputrte;
		ListCell   *ll;

		++rt_index;
		switch (rte->rtekind)
		{
			case RTE_RELATION:

				/*
				 * Grab the appropriate lock type for the relation, and do not
				 * release it until end of transaction. This protects the
				 * rewriter and planner against schema changes mid-query.
				 *
				 * If the relation is the query's result relation, then we
				 * need RowExclusiveLock.  Otherwise, check to see if the
				 * relation is accessed FOR UPDATE/SHARE or not.  We can't
				 * just grab AccessShareLock because then the executor would
				 * be trying to upgrade the lock, leading to possible
				 * deadlocks.
				 */
				if (rt_index == parsetree->resultRelation)
					lockmode = RowExclusiveLock;
				else if (list_member_int(parsetree->rowMarks, rt_index))
					lockmode = RowShareLock;
				else
					lockmode = AccessShareLock;

				rel = heap_open(rte->relid, lockmode);
				heap_close(rel, NoLock);
				break;

			case RTE_JOIN:

				/*
				 * Scan the join's alias var list to see if any columns have
				 * been dropped, and if so replace those Vars with NULL
				 * Consts.
				 *
				 * Since a join has only two inputs, we can expect to see
				 * multiple references to the same input RTE; optimize away
				 * multiple fetches.
				 */
				newaliasvars = NIL;
				curinputvarno = 0;
				curinputrte = NULL;
				foreach(ll, rte->joinaliasvars)
				{
					Var		   *aliasvar = (Var *) lfirst(ll);

					/*
					 * If the list item isn't a simple Var, then it must
					 * represent a merged column, ie a USING column, and so it
					 * couldn't possibly be dropped, since it's referenced in
					 * the join clause.  (Conceivably it could also be a NULL
					 * constant already?  But that's OK too.)
					 */
					if (IsA(aliasvar, Var))
					{
						/*
						 * The elements of an alias list have to refer to
						 * earlier RTEs of the same rtable, because that's the
						 * order the planner builds things in.	So we already
						 * processed the referenced RTE, and so it's safe to
						 * use get_rte_attribute_is_dropped on it. (This might
						 * not hold after rewriting or planning, but it's OK
						 * to assume here.)
						 */
						Assert(aliasvar->varlevelsup == 0);
						if (aliasvar->varno != curinputvarno)
						{
							curinputvarno = aliasvar->varno;
							if (curinputvarno >= rt_index)
								elog(ERROR, "unexpected varno %d in JOIN RTE %d",
									 curinputvarno, rt_index);
							curinputrte = rt_fetch(curinputvarno,
												   parsetree->rtable);
						}
						if (get_rte_attribute_is_dropped(curinputrte,
														 aliasvar->varattno))
						{
							/*
							 * can't use vartype here, since that might be a
							 * now-dropped type OID, but it doesn't really
							 * matter what type the Const claims to be.
							 */
							aliasvar = (Var *) makeNullConst(INT4OID);
						}
					}
					newaliasvars = lappend(newaliasvars, aliasvar);
				}
				rte->joinaliasvars = newaliasvars;
				break;

			case RTE_SUBQUERY:

				/*
				 * The subquery RTE itself is all right, but we have to
				 * recurse to process the represented subquery.
				 */
				AcquireRewriteLocks(rte->subquery);
				break;

			default:
				/* ignore other types of RTEs */
				break;
		}
	}

	/*
	 * Recurse into sublink subqueries, too.  But we already did the ones in
	 * the rtable.
	 */
	if (parsetree->hasSubLinks)
		query_tree_walker(parsetree, acquireLocksOnSubLinks, NULL,
						  QTW_IGNORE_RT_SUBQUERIES);
}

/*
 * Walker to find sublink subqueries for AcquireRewriteLocks
 */
static bool
acquireLocksOnSubLinks(Node *node, void *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, SubLink))
	{
		SubLink    *sub = (SubLink *) node;

		/* Do what we came for */
		AcquireRewriteLocks((Query *) sub->subselect);
		/* Fall through to process lefthand args of SubLink */
	}

	/*
	 * Do NOT recurse into Query nodes, because AcquireRewriteLocks already
	 * processed subselects of subselects for us.
	 */
	return expression_tree_walker(node, acquireLocksOnSubLinks, context);
}


/*
 * rewriteRuleAction -
 *	  Rewrite the rule action with appropriate qualifiers (taken from
 *	  the triggering query).
 */
static Query *
rewriteRuleAction(Query *parsetree,
				  Query *rule_action,
				  Node *rule_qual,
				  int rt_index,
				  CmdType event)
{
	int			current_varno,
				new_varno;
	int			rt_length;
	Query	   *sub_action;
	Query	  **sub_action_ptr;

	/*
	 * Make modifiable copies of rule action and qual (what we're passed are
	 * the stored versions in the relcache; don't touch 'em!).
	 */
	rule_action = (Query *) copyObject(rule_action);
	rule_qual = (Node *) copyObject(rule_qual);

	/*
	 * Acquire necessary locks and fix any deleted JOIN RTE entries.
	 */
	AcquireRewriteLocks(rule_action);
	(void) acquireLocksOnSubLinks(rule_qual, NULL);

	current_varno = rt_index;
	rt_length = list_length(parsetree->rtable);
	new_varno = PRS2_NEW_VARNO + rt_length;

	/*
	 * Adjust rule action and qual to offset its varnos, so that we can merge
	 * its rtable with the main parsetree's rtable.
	 *
	 * If the rule action is an INSERT...SELECT, the OLD/NEW rtable entries
	 * will be in the SELECT part, and we have to modify that rather than the
	 * top-level INSERT (kluge!).
	 */
	sub_action = getInsertSelectQuery(rule_action, &sub_action_ptr);

	OffsetVarNodes((Node *) sub_action, rt_length, 0);
	OffsetVarNodes(rule_qual, rt_length, 0);
	/* but references to *OLD* should point at original rt_index */
	ChangeVarNodes((Node *) sub_action,
				   PRS2_OLD_VARNO + rt_length, rt_index, 0);
	ChangeVarNodes(rule_qual,
				   PRS2_OLD_VARNO + rt_length, rt_index, 0);

	/*
	 * Generate expanded rtable consisting of main parsetree's rtable plus
	 * rule action's rtable; this becomes the complete rtable for the rule
	 * action.	Some of the entries may be unused after we finish rewriting,
	 * but we leave them all in place for two reasons:
	 *
	 * We'd have a much harder job to adjust the query's varnos if we
	 * selectively removed RT entries.
	 *
	 * If the rule is INSTEAD, then the original query won't be executed at
	 * all, and so its rtable must be preserved so that the executor will do
	 * the correct permissions checks on it.
	 *
	 * RT entries that are not referenced in the completed jointree will be
	 * ignored by the planner, so they do not affect query semantics.  But any
	 * permissions checks specified in them will be applied during executor
	 * startup (see ExecCheckRTEPerms()).  This allows us to check that the
	 * caller has, say, insert-permission on a view, when the view is not
	 * semantically referenced at all in the resulting query.
	 *
	 * When a rule is not INSTEAD, the permissions checks done on its copied
	 * RT entries will be redundant with those done during execution of the
	 * original query, but we don't bother to treat that case differently.
	 *
	 * NOTE: because planner will destructively alter rtable, we must ensure
	 * that rule action's rtable is separate and shares no substructure with
	 * the main rtable.  Hence do a deep copy here.
	 */
	sub_action->rtable = list_concat((List *) copyObject(parsetree->rtable),
									 sub_action->rtable);

	/*
	 * Each rule action's jointree should be the main parsetree's jointree
	 * plus that rule's jointree, but usually *without* the original rtindex
	 * that we're replacing (if present, which it won't be for INSERT). Note
	 * that if the rule action refers to OLD, its jointree will add a
	 * reference to rt_index.  If the rule action doesn't refer to OLD, but
	 * either the rule_qual or the user query quals do, then we need to keep
	 * the original rtindex in the jointree to provide data for the quals.	We
	 * don't want the original rtindex to be joined twice, however, so avoid
	 * keeping it if the rule action mentions it.
	 *
	 * As above, the action's jointree must not share substructure with the
	 * main parsetree's.
	 */
	if (sub_action->commandType != CMD_UTILITY)
	{
		bool		keeporig;
		List	   *newjointree;

		Assert(sub_action->jointree != NULL);
		keeporig = (!rangeTableEntry_used((Node *) sub_action->jointree,
										  rt_index, 0)) &&
			(rangeTableEntry_used(rule_qual, rt_index, 0) ||
			 rangeTableEntry_used(parsetree->jointree->quals, rt_index, 0));
		newjointree = adjustJoinTreeList(parsetree, !keeporig, rt_index);
		if (newjointree != NIL)
		{
			/*
			 * If sub_action is a setop, manipulating its jointree will do no
			 * good at all, because the jointree is dummy.	(Perhaps someday
			 * we could push the joining and quals down to the member
			 * statements of the setop?)
			 */
			if (sub_action->setOperations != NULL)
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("conditional UNION/INTERSECT/EXCEPT statements are not implemented")));

			sub_action->jointree->fromlist =
				list_concat(newjointree, sub_action->jointree->fromlist);

			/*
			 * There could have been some SubLinks in newjointree, in which
			 * case we'd better mark the sub_action correctly.
			 */
			if (parsetree->hasSubLinks && !sub_action->hasSubLinks)
				sub_action->hasSubLinks =
					checkExprHasSubLink((Node *) newjointree);
		}
	}

	/*
	 * Event Qualification forces copying of parsetree and splitting into two
	 * queries one w/rule_qual, one w/NOT rule_qual. Also add user query qual
	 * onto rule action
	 */
	AddQual(sub_action, rule_qual);

	AddQual(sub_action, parsetree->jointree->quals);

	/*
	 * Rewrite new.attribute w/ right hand side of target-list entry for
	 * appropriate field name in insert/update.
	 *
	 * KLUGE ALERT: since ResolveNew returns a mutated copy, we can't just
	 * apply it to sub_action; we have to remember to update the sublink
	 * inside rule_action, too.
	 */
	if ((event == CMD_INSERT || event == CMD_UPDATE) &&