rewritehandler.c

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/*-------------------------------------------------------------------------
 *
 * rewriteHandler.c
 *		Primary module of query rewriter.
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.130.2.1 2004/01/14 03:39:29 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 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 void markQueryForUpdate(Query *qry, bool skipOldNew);
static List *matchLocks(CmdType event, RuleLock *rulelocks,
		   int varno, Query *parsetree);
static Query *fireRIRrules(Query *parsetree, List *activeRIRs);


/*
 * 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);

	current_varno = rt_index;
	rt_length = 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 = nconc((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 =
				nconc(newjointree, sub_action->jointree->fromlist);
		}
	}

	/*
	 * We copy the qualifications of the parsetree to the action and vice
	 * versa. So force hasSubLinks if one of them has it. If this is not
	 * right, the flag will get cleared later, but we mustn't risk having
	 * it not set when it needs to be.	(XXX this should probably be
	 * handled by AddQual and friends, not here...)
	 */
	if (parsetree->hasSubLinks)
		sub_action->hasSubLinks = TRUE;
	else if (sub_action->hasSubLinks)
		parsetree->hasSubLinks = TRUE;

	/*
	 * 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)
	{
		sub_action = (Query *) ResolveNew((Node *) sub_action,
										  new_varno,
										  0,
										  parsetree->targetList,
										  event,
										  current_varno);
		if (sub_action_ptr)
			*sub_action_ptr = sub_action;
		else
			rule_action = sub_action;
	}

	return rule_action;
}

/*
 * Copy the query's jointree list, and optionally attempt to remove any
 * occurrence of the given rt_index as a top-level join item (we do not look
 * for it within join items; this is OK because we are only expecting to find
 * it as an UPDATE or DELETE target relation, which will be at the top level
 * of the join).  Returns modified jointree list --- this is a separate copy
 * sharing no nodes with the original.
 */
static List *
adjustJoinTreeList(Query *parsetree, bool removert, int rt_index)
{
	List	   *newjointree = copyObject(parsetree->jointree->fromlist);
	List	   *jjt;

	if (removert)
	{
		foreach(jjt, newjointree)
		{
			RangeTblRef *rtr = lfirst(jjt);

			if (IsA(rtr, RangeTblRef) &&
				rtr->rtindex == rt_index)
			{
				newjointree = lremove(rtr, newjointree);
				/* foreach is safe because we exit loop after lremove... */
				break;
			}
		}
	}
	return newjointree;
}


/*
 * rewriteTargetList - rewrite INSERT/UPDATE targetlist into standard form
 *
 * This has the following responsibilities:
 *
 * 1. For an INSERT, add tlist entries to compute default values for any
 * attributes that have defaults and are not assigned to in the given tlist.
 * (We do not insert anything for default-less attributes, however.  The
 * planner will later insert NULLs for them, but there's no reason to slow
 * down rewriter processing with extra tlist nodes.)  Also, for both INSERT
 * and UPDATE, replace explicit DEFAULT specifications with column default
 * expressions.
 *
 * 2. Merge multiple entries for the same target attribute, or declare error
 * if we can't.  Presently, multiple entries are only allowed for UPDATE of
 * an array field, for example "UPDATE table SET foo[2] = 42, foo[4] = 43".
 * We can merge such operations into a single assignment op.  Essentially,
 * the expression we want to produce in this case is like
 *		foo = array_set(array_set(foo, 2, 42), 4, 43)
 *
 * 3. Sort the tlist into standard order: non-junk fields in order by resno,
 * then junk fields (these in no particular order).
 *
 * We must do items 1 and 2 before firing rewrite rules, else rewritten
 * references to NEW.foo will produce wrong or incomplete results.	Item 3
 * is not needed for rewriting, but will be needed by the planner, and we
 * can do it essentially for free while handling items 1 and 2.
 */
static void
rewriteTargetList(Query *parsetree, Relation target_relation)
{
	CmdType		commandType = parsetree->commandType;
	List	   *tlist = parsetree->targetList;
	List	   *new_tlist = NIL;
	int			attrno,
				numattrs;
	List	   *temp;

	/*
	 * Scan the tuple description in the relation's relcache entry to make
	 * sure we have all the user attributes in the right order.
	 */
	numattrs = RelationGetNumberOfAttributes(target_relation);

	for (attrno = 1; attrno <= numattrs; attrno++)
	{
		Form_pg_attribute att_tup = target_relation->rd_att->attrs[attrno - 1];
		TargetEntry *new_tle = NULL;

		/* We can ignore deleted attributes */
		if (att_tup->attisdropped)
			continue;

		/*
		 * Look for targetlist entries matching this attr.
		 *
		 * Junk attributes are not candidates to be matched.
		 */
		foreach(temp, tlist)
		{
			TargetEntry *old_tle = (TargetEntry *) lfirst(temp);
			Resdom	   *resdom = old_tle->resdom;

			if (!resdom->resjunk && resdom->resno == attrno)
			{
				new_tle = process_matched_tle(old_tle, new_tle,
											  NameStr(att_tup->attname));
				/* keep scanning to detect multiple assignments to attr */
			}
		}

		/*
		 * Handle the two cases where we need to insert a default
		 * expression: it's an INSERT and there's no tlist entry for the
		 * column, or the tlist entry is a DEFAULT placeholder node.
		 */
		if ((new_tle == NULL && commandType == CMD_INSERT) ||
		  (new_tle && new_tle->expr && IsA(new_tle->expr, SetToDefault)))
		{
			Node	   *new_expr;

			new_expr = build_column_default(target_relation, attrno);

			/*
			 * If there is no default (ie, default is effectively NULL),
			 * we can omit the tlist entry in the INSERT case, since the
			 * planner can insert a NULL for itself, and there's no point
			 * in spending any more rewriter cycles on the entry.  But in
			 * the UPDATE case we've got to explicitly set the column to
			 * NULL.
			 */
			if (!new_expr)
			{
				if (commandType == CMD_INSERT)
					new_tle = NULL;
				else
				{
					new_expr = (Node *) makeConst(att_tup->atttypid,
												  att_tup->attlen,
												  (Datum) 0,
												  true, /* isnull */
												  att_tup->attbyval);
					/* this is to catch a NOT NULL domain constraint */
					new_expr = coerce_to_domain(new_expr,
												InvalidOid,
												att_tup->atttypid,
												COERCE_IMPLICIT_CAST);
				}
			}

			if (new_expr)
				new_tle = makeTargetEntry(makeResdom(attrno,
													 att_tup->atttypid,
													 att_tup->atttypmod,
									  pstrdup(NameStr(att_tup->attname)),
													 false),
										  (Expr *) new_expr);
		}

		if (new_tle)
			new_tlist = lappend(new_tlist, new_tle);
	}

	/*
	 * Copy all resjunk tlist entries to the end of the new tlist, and
	 * assign them resnos above the last real resno.
	 *
	 * Typical junk entries include ORDER BY or GROUP BY expressions (are
	 * these actually possible in an INSERT or UPDATE?), system attribute
	 * references, etc.
	 */
	foreach(temp, tlist)
	{
		TargetEntry *old_tle = (TargetEntry *) lfirst(temp);
		Resdom	   *resdom = old_tle->resdom;

		if (resdom->resjunk)
		{
			/* Get the resno right, but don't copy unnecessarily */
			if (resdom->resno != attrno)
			{
				resdom = (Resdom *) copyObject((Node *) resdom);
				resdom->resno = attrno;
				old_tle = makeTargetEntry(resdom, old_tle->expr);
			}
			new_tlist = lappend(new_tlist, old_tle);
			attrno++;
		}
		else
		{
			/* Let's just make sure we processed all the non-junk items */
			if (resdom->resno < 1 || resdom->resno > numattrs)
				elog(ERROR, "bogus resno %d in targetlist", resdom->resno);
		}
	}

	parsetree->targetList = new_tlist;
}


/*
 * Convert a matched TLE from the original tlist into a correct new TLE.
 *
 * This routine detects and handles multiple assignments to the same target
 * attribute.  (The attribute name is needed only for error messages.)
 */
static TargetEntry *
process_matched_tle(TargetEntry *src_tle,
					TargetEntry *prior_tle,
					const char *attrName)
{
	Resdom	   *resdom = src_tle->resdom;
	Node	   *priorbottom;
	ArrayRef   *newexpr;

	if (prior_tle == NULL)
	{
		/*
		 * Normal case where this is the first assignment to the
		 * attribute.
		 */
		return src_tle;
	}

	/*
	 * Multiple assignments to same attribute.	Allow only if all are
	 * array-assign operators with same bottom array object.
	 */
	if (src_tle->expr == NULL || !IsA(src_tle->expr, ArrayRef) ||
		((ArrayRef *) src_tle->expr)->refassgnexpr == NULL ||
		prior_tle->expr == NULL || !IsA(prior_tle->expr, ArrayRef) ||