lsyscache.c

/*-------------------------------------------------------------------------
 *
 * lsyscache.c
 *	  Convenience routines for common queries in the system catalog cache.
 *
 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/utils/cache/lsyscache.c
 *
 * NOTES
 *	  Eventually, the index information should go through here, too.
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/hash.h"
#include "access/nbtree.h"
#include "bootstrap/bootstrap.h"
#include "catalog/pg_amop.h"
#include "catalog/pg_amproc.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_statistic.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/fmgroids.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "utils/typcache.h"

/* Hook for plugins to get control in get_attavgwidth() */
get_attavgwidth_hook_type get_attavgwidth_hook = NULL;


/*				---------- AMOP CACHES ----------						 */

/*
 * op_in_opfamily
 *
 *		Return t iff operator 'opno' is in operator family 'opfamily'.
 *
 * This function only considers search operators, not ordering operators.
 */
bool
op_in_opfamily(Oid opno, Oid opfamily)
{
	return SearchSysCacheExists3(AMOPOPID,
								 ObjectIdGetDatum(opno),
								 CharGetDatum(AMOP_SEARCH),
								 ObjectIdGetDatum(opfamily));
}

/*
 * get_op_opfamily_strategy
 *
 *		Get the operator's strategy number within the specified opfamily,
 *		or 0 if it's not a member of the opfamily.
 *
 * This function only considers search operators, not ordering operators.
 */
int
get_op_opfamily_strategy(Oid opno, Oid opfamily)
{
	HeapTuple	tp;
	Form_pg_amop amop_tup;
	int			result;

	tp = SearchSysCache3(AMOPOPID,
						 ObjectIdGetDatum(opno),
						 CharGetDatum(AMOP_SEARCH),
						 ObjectIdGetDatum(opfamily));
	if (!HeapTupleIsValid(tp))
		return 0;
	amop_tup = (Form_pg_amop) GETSTRUCT(tp);
	result = amop_tup->amopstrategy;
	ReleaseSysCache(tp);
	return result;
}

/*
 * get_op_opfamily_sortfamily
 *
 *		If the operator is an ordering operator within the specified opfamily,
 *		return its amopsortfamily OID; else return InvalidOid.
 */
Oid
get_op_opfamily_sortfamily(Oid opno, Oid opfamily)
{
	HeapTuple	tp;
	Form_pg_amop amop_tup;
	Oid			result;

	tp = SearchSysCache3(AMOPOPID,
						 ObjectIdGetDatum(opno),
						 CharGetDatum(AMOP_ORDER),
						 ObjectIdGetDatum(opfamily));
	if (!HeapTupleIsValid(tp))
		return InvalidOid;
	amop_tup = (Form_pg_amop) GETSTRUCT(tp);
	result = amop_tup->amopsortfamily;
	ReleaseSysCache(tp);
	return result;
}

/*
 * get_op_opfamily_properties
 *
 *		Get the operator's strategy number and declared input data types
 *		within the specified opfamily.
 *
 * Caller should already have verified that opno is a member of opfamily,
 * therefore we raise an error if the tuple is not found.
 */
void
get_op_opfamily_properties(Oid opno, Oid opfamily, bool ordering_op,
						   int *strategy,
						   Oid *lefttype,
						   Oid *righttype)
{
	HeapTuple	tp;
	Form_pg_amop amop_tup;

	tp = SearchSysCache3(AMOPOPID,
						 ObjectIdGetDatum(opno),
						 CharGetDatum(ordering_op ? AMOP_ORDER : AMOP_SEARCH),
						 ObjectIdGetDatum(opfamily));
	if (!HeapTupleIsValid(tp))
		elog(ERROR, "operator %u is not a member of opfamily %u",
			 opno, opfamily);
	amop_tup = (Form_pg_amop) GETSTRUCT(tp);
	*strategy = amop_tup->amopstrategy;
	*lefttype = amop_tup->amoplefttype;
	*righttype = amop_tup->amoprighttype;
	ReleaseSysCache(tp);
}

/*
 * get_opfamily_member
 *		Get the OID of the operator that implements the specified strategy
 *		with the specified datatypes for the specified opfamily.
 *
 * Returns InvalidOid if there is no pg_amop entry for the given keys.
 */
Oid
get_opfamily_member(Oid opfamily, Oid lefttype, Oid righttype,
					int16 strategy)
{
	HeapTuple	tp;
	Form_pg_amop amop_tup;
	Oid			result;

	tp = SearchSysCache4(AMOPSTRATEGY,
						 ObjectIdGetDatum(opfamily),
						 ObjectIdGetDatum(lefttype),
						 ObjectIdGetDatum(righttype),
						 Int16GetDatum(strategy));
	if (!HeapTupleIsValid(tp))
		return InvalidOid;
	amop_tup = (Form_pg_amop) GETSTRUCT(tp);
	result = amop_tup->amopopr;
	ReleaseSysCache(tp);
	return result;
}

/*
 * get_ordering_op_properties
 *		Given the OID of an ordering operator (a btree "<" or ">" operator),
 *		determine its opfamily, its declared input datatype, and its
 *		strategy number (BTLessStrategyNumber or BTGreaterStrategyNumber).
 *
 * Returns TRUE if successful, FALSE if no matching pg_amop entry exists.
 * (This indicates that the operator is not a valid ordering operator.)
 *
 * Note: the operator could be registered in multiple families, for example
 * if someone were to build a "reverse sort" opfamily.	This would result in
 * uncertainty as to whether "ORDER BY USING op" would default to NULLS FIRST
 * or NULLS LAST, as well as inefficient planning due to failure to match up
 * pathkeys that should be the same.  So we want a determinate result here.
 * Because of the way the syscache search works, we'll use the interpretation
 * associated with the opfamily with smallest OID, which is probably
 * determinate enough.	Since there is no longer any particularly good reason
 * to build reverse-sort opfamilies, it doesn't seem worth expending any
 * additional effort on ensuring consistency.
 */
bool
get_ordering_op_properties(Oid opno,
						   Oid *opfamily, Oid *opcintype, int16 *strategy)
{
	bool		result = false;
	CatCList   *catlist;
	int			i;

	/* ensure outputs are initialized on failure */
	*opfamily = InvalidOid;
	*opcintype = InvalidOid;
	*strategy = 0;

	/*
	 * Search pg_amop to see if the target operator is registered as the "<"
	 * or ">" operator of any btree opfamily.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	tuple = &catlist->members[i]->tuple;
		Form_pg_amop aform = (Form_pg_amop) GETSTRUCT(tuple);

		/* must be btree */
		if (aform->amopmethod != BTREE_AM_OID)
			continue;

		if (aform->amopstrategy == BTLessStrategyNumber ||
			aform->amopstrategy == BTGreaterStrategyNumber)
		{
			/* Found it ... should have consistent input types */
			if (aform->amoplefttype == aform->amoprighttype)
			{
				/* Found a suitable opfamily, return info */
				*opfamily = aform->amopfamily;
				*opcintype = aform->amoplefttype;
				*strategy = aform->amopstrategy;
				result = true;
				break;
			}
		}
	}

	ReleaseSysCacheList(catlist);

	return result;
}

/*
 * get_compare_function_for_ordering_op
 *		Get the OID of the datatype-specific btree comparison function
 *		associated with an ordering operator (a "<" or ">" operator).
 *
 * *cmpfunc receives the comparison function OID.
 * *reverse is set FALSE if the operator is "<", TRUE if it's ">"
 * (indicating the comparison result must be negated before use).
 *
 * Returns TRUE if successful, FALSE if no btree function can be found.
 * (This indicates that the operator is not a valid ordering operator.)
 */
bool
get_compare_function_for_ordering_op(Oid opno, Oid *cmpfunc, bool *reverse)
{
	Oid			opfamily;
	Oid			opcintype;
	int16		strategy;

	/* Find the operator in pg_amop */
	if (get_ordering_op_properties(opno,
								   &opfamily, &opcintype, &strategy))
	{
		/* Found a suitable opfamily, get matching support function */
		*cmpfunc = get_opfamily_proc(opfamily,
									 opcintype,
									 opcintype,
									 BTORDER_PROC);

		if (!OidIsValid(*cmpfunc))		/* should not happen */
			elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
				 BTORDER_PROC, opcintype, opcintype, opfamily);
		*reverse = (strategy == BTGreaterStrategyNumber);
		return true;
	}

	/* ensure outputs are set on failure */
	*cmpfunc = InvalidOid;

	*reverse = false;
	return false;
}

/*
 * get_equality_op_for_ordering_op
 *		Get the OID of the datatype-specific btree equality operator
 *		associated with an ordering operator (a "<" or ">" operator).
 *
 * If "reverse" isn't NULL, also set *reverse to FALSE if the operator is "<",
 * TRUE if it's ">"
 *
 * Returns InvalidOid if no matching equality operator can be found.
 * (This indicates that the operator is not a valid ordering operator.)
 */
Oid
get_equality_op_for_ordering_op(Oid opno, bool *reverse)
{
	Oid			result = InvalidOid;
	Oid			opfamily;
	Oid			opcintype;
	int16		strategy;

	/* Find the operator in pg_amop */
	if (get_ordering_op_properties(opno,
								   &opfamily, &opcintype, &strategy))
	{
		/* Found a suitable opfamily, get matching equality operator */
		result = get_opfamily_member(opfamily,
									 opcintype,
									 opcintype,
									 BTEqualStrategyNumber);
		if (reverse)
			*reverse = (strategy == BTGreaterStrategyNumber);
	}

	return result;
}

/*
 * get_ordering_op_for_equality_op
 *		Get the OID of a datatype-specific btree ordering operator
 *		associated with an equality operator.  (If there are multiple
 *		possibilities, assume any one will do.)
 *
 * This function is used when we have to sort data before unique-ifying,
 * and don't much care which sorting op is used as long as it's compatible
 * with the intended equality operator.  Since we need a sorting operator,
 * it should be single-data-type even if the given operator is cross-type.
 * The caller specifies whether to find an op for the LHS or RHS data type.
 *
 * Returns InvalidOid if no matching ordering operator can be found.
 */
Oid
get_ordering_op_for_equality_op(Oid opno, bool use_lhs_type)
{
	Oid			result = InvalidOid;
	CatCList   *catlist;
	int			i;

	/*
	 * Search pg_amop to see if the target operator is registered as the "="
	 * operator of any btree opfamily.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	tuple = &catlist->members[i]->tuple;
		Form_pg_amop aform = (Form_pg_amop) GETSTRUCT(tuple);

		/* must be btree */
		if (aform->amopmethod != BTREE_AM_OID)
			continue;

		if (aform->amopstrategy == BTEqualStrategyNumber)
		{
			/* Found a suitable opfamily, get matching ordering operator */
			Oid			typid;

			typid = use_lhs_type ? aform->amoplefttype : aform->amoprighttype;
			result = get_opfamily_member(aform->amopfamily,
										 typid, typid,
										 BTLessStrategyNumber);
			if (OidIsValid(result))
				break;
			/* failure probably shouldn't happen, but keep looking if so */
		}
	}

	ReleaseSysCacheList(catlist);

	return result;
}

/*
 * get_mergejoin_opfamilies
 *		Given a putatively mergejoinable operator, return a list of the OIDs
 *		of the btree opfamilies in which it represents equality.
 *
 * It is possible (though at present unusual) for an operator to be equality
 * in more than one opfamily, hence the result is a list.  This also lets us
 * return NIL if the operator is not found in any opfamilies.
 *
 * The planner currently uses simple equal() tests to compare the lists
 * returned by this function, which makes the list order relevant, though
 * strictly speaking it should not be.	Because of the way syscache list
 * searches are handled, in normal operation the result will be sorted by OID
 * so everything works fine.  If running with system index usage disabled,
 * the result ordering is unspecified and hence the planner might fail to
 * recognize optimization opportunities ... but that's hardly a scenario in
 * which performance is good anyway, so there's no point in expending code
 * or cycles here to guarantee the ordering in that case.
 */
List *
get_mergejoin_opfamilies(Oid opno)
{
	List	   *result = NIL;
	CatCList   *catlist;
	int			i;

	/*
	 * Search pg_amop to see if the target operator is registered as the "="
	 * operator of any btree opfamily.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	tuple = &catlist->members[i]->tuple;
		Form_pg_amop aform = (Form_pg_amop) GETSTRUCT(tuple);

		/* must be btree equality */
		if (aform->amopmethod == BTREE_AM_OID &&
			aform->amopstrategy == BTEqualStrategyNumber)
			result = lappend_oid(result, aform->amopfamily);
	}

	ReleaseSysCacheList(catlist);

	return result;
}

/*
 * get_compatible_hash_operators
 *		Get the OID(s) of hash equality operator(s) compatible with the given
 *		operator, but operating on its LHS and/or RHS datatype.
 *
 * An operator for the LHS type is sought and returned into *lhs_opno if
 * lhs_opno isn't NULL.  Similarly, an operator for the RHS type is sought
 * and returned into *rhs_opno if rhs_opno isn't NULL.
 *
 * If the given operator is not cross-type, the results should be the same
 * operator, but in cross-type situations they will be different.
 *
 * Returns true if able to find the requested operator(s), false if not.
 * (This indicates that the operator should not have been marked oprcanhash.)
 */
bool
get_compatible_hash_operators(Oid opno,
							  Oid *lhs_opno, Oid *rhs_opno)
{
	bool		result = false;
	CatCList   *catlist;
	int			i;

	/* Ensure output args are initialized on failure */
	if (lhs_opno)
		*lhs_opno = InvalidOid;
	if (rhs_opno)
		*rhs_opno = InvalidOid;

	/*
	 * Search pg_amop to see if the target operator is registered as the "="
	 * operator of any hash opfamily.  If the operator is registered in
	 * multiple opfamilies, assume we can use any one.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	tuple = &catlist->members[i]->tuple;
		Form_pg_amop aform = (Form_pg_amop) GETSTRUCT(tuple);

		if (aform->amopmethod == HASH_AM_OID &&
			aform->amopstrategy == HTEqualStrategyNumber)
		{
			/* No extra lookup needed if given operator is single-type */
			if (aform->amoplefttype == aform->amoprighttype)
			{
				if (lhs_opno)
					*lhs_opno = opno;
				if (rhs_opno)
					*rhs_opno = opno;
				result = true;
				break;
			}

			/*
			 * Get the matching single-type operator(s).  Failure probably
			 * shouldn't happen --- it implies a bogus opfamily --- but
			 * continue looking if so.
			 */
			if (lhs_opno)
			{
				*lhs_opno = get_opfamily_member(aform->amopfamily,
												aform->amoplefttype,
												aform->amoplefttype,
												HTEqualStrategyNumber);
				if (!OidIsValid(*lhs_opno))
					continue;
				/* Matching LHS found, done if caller doesn't want RHS */
				if (!rhs_opno)
				{
					result = true;
					break;
				}
			}
			if (rhs_opno)
			{
				*rhs_opno = get_opfamily_member(aform->amopfamily,
												aform->amoprighttype,
												aform->amoprighttype,
												HTEqualStrategyNumber);
				if (!OidIsValid(*rhs_opno))
				{
					/* Forget any LHS operator from this opfamily */
					if (lhs_opno)
						*lhs_opno = InvalidOid;
					continue;
				}
				/* Matching RHS found, so done */
				result = true;
				break;
			}
		}
	}

	ReleaseSysCacheList(catlist);

	return result;
}

/*
 * get_op_hash_functions
 *		Get the OID(s) of hash support function(s) compatible with the given
 *		operator, operating on its LHS and/or RHS datatype as required.
 *
 * A function for the LHS type is sought and returned into *lhs_procno if
 * lhs_procno isn't NULL.  Similarly, a function for the RHS type is sought
 * and returned into *rhs_procno if rhs_procno isn't NULL.
 *
 * If the given operator is not cross-type, the results should be the same
 * function, but in cross-type situations they will be different.
 *
 * Returns true if able to find the requested function(s), false if not.
 * (This indicates that the operator should not have been marked oprcanhash.)
 */
bool
get_op_hash_functions(Oid opno,
					  RegProcedure *lhs_procno, RegProcedure *rhs_procno)
{
	bool		result = false;
	CatCList   *catlist;
	int			i;

	/* Ensure output args are initialized on failure */
	if (lhs_procno)
		*lhs_procno = InvalidOid;
	if (rhs_procno)
		*rhs_procno = InvalidOid;

	/*
	 * Search pg_amop to see if the target operator is registered as the "="
	 * operator of any hash opfamily.  If the operator is registered in
	 * multiple opfamilies, assume we can use any one.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	tuple = &catlist->members[i]->tuple;
		Form_pg_amop aform = (Form_pg_amop) GETSTRUCT(tuple);

		if (aform->amopmethod == HASH_AM_OID &&
			aform->amopstrategy == HTEqualStrategyNumber)
		{
			/*
			 * Get the matching support function(s).  Failure probably
			 * shouldn't happen --- it implies a bogus opfamily --- but
			 * continue looking if so.
			 */
			if (lhs_procno)
			{
				*lhs_procno = get_opfamily_proc(aform->amopfamily,
												aform->amoplefttype,
												aform->amoplefttype,
												HASHPROC);
				if (!OidIsValid(*lhs_procno))
					continue;
				/* Matching LHS found, done if caller doesn't want RHS */
				if (!rhs_procno)
				{
					result = true;
					break;
				}
				/* Only one lookup needed if given operator is single-type */
				if (aform->amoplefttype == aform->amoprighttype)
				{
					*rhs_procno = *lhs_procno;
					result = true;
					break;
				}
			}
			if (rhs_procno)
			{
				*rhs_procno = get_opfamily_proc(aform->amopfamily,
												aform->amoprighttype,
												aform->amoprighttype,
												HASHPROC);
				if (!OidIsValid(*rhs_procno))
				{
					/* Forget any LHS function from this opfamily */
					if (lhs_procno)
						*lhs_procno = InvalidOid;
					continue;
				}
				/* Matching RHS found, so done */
				result = true;
				break;
			}
		}
	}

	ReleaseSysCacheList(catlist);

	return result;
}

/*
 * get_op_btree_interpretation
 *		Given an operator's OID, find out which btree opfamilies it belongs to,
 *		and what strategy number it has within each one.  The results are
 *		returned as an OID list and a parallel integer list.
 *
 * In addition to the normal btree operators, we consider a <> operator to be
 * a "member" of an opfamily if its negator is an equality operator of the
 * opfamily.  ROWCOMPARE_NE is returned as the strategy number for this case.
 */
void
get_op_btree_interpretation(Oid opno, List **opfamilies, List **opstrats)
{
	CatCList   *catlist;
	bool		op_negated;
	int			i;

	*opfamilies = NIL;
	*opstrats = NIL;

	/*
	 * Find all the pg_amop entries containing the operator.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno));

	/*
	 * If we can't find any opfamily containing the op, perhaps it is a <>
	 * operator.  See if it has a negator that is in an opfamily.
	 */
	op_negated = false;
	if (catlist->n_members == 0)
	{
		Oid			op_negator = get_negator(opno);

		if (OidIsValid(op_negator))
		{
			op_negated = true;
			ReleaseSysCacheList(catlist);
			catlist = SearchSysCacheList1(AMOPOPID,
										  ObjectIdGetDatum(op_negator));
		}
	}

	/* Now search the opfamilies */
	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	op_tuple = &catlist->members[i]->tuple;
		Form_pg_amop op_form = (Form_pg_amop) GETSTRUCT(op_tuple);
		Oid			opfamily_id;
		StrategyNumber op_strategy;

		/* must be btree */
		if (op_form->amopmethod != BTREE_AM_OID)
			continue;

		/* Get the operator's btree strategy number */
		opfamily_id = op_form->amopfamily;
		op_strategy = (StrategyNumber) op_form->amopstrategy;
		Assert(op_strategy >= 1 && op_strategy <= 5);

		if (op_negated)
		{
			/* Only consider negators that are = */
			if (op_strategy != BTEqualStrategyNumber)
				continue;
			op_strategy = ROWCOMPARE_NE;
		}

		*opfamilies = lappend_oid(*opfamilies, opfamily_id);
		*opstrats = lappend_int(*opstrats, op_strategy);
	}

	ReleaseSysCacheList(catlist);
}

/*
 * equality_ops_are_compatible
 *		Return TRUE if the two given equality operators have compatible
 *		semantics.
 *
 * This is trivially true if they are the same operator.  Otherwise,
 * we look to see if they can be found in the same btree or hash opfamily.
 * Either finding allows us to assume that they have compatible notions
 * of equality.  (The reason we need to do these pushups is that one might
 * be a cross-type operator; for instance int24eq vs int4eq.)
 */
bool
equality_ops_are_compatible(Oid opno1, Oid opno2)
{
	bool		result;
	CatCList   *catlist;
	int			i;

	/* Easy if they're the same operator */
	if (opno1 == opno2)
		return true;

	/*
	 * We search through all the pg_amop entries for opno1.
	 */
	catlist = SearchSysCacheList1(AMOPOPID, ObjectIdGetDatum(opno1));

	result = false;
	for (i = 0; i < catlist->n_members; i++)
	{
		HeapTuple	op_tuple = &catlist->members[i]->tuple;
		Form_pg_amop op_form = (Form_pg_amop) GETSTRUCT(op_tuple);

		/* must be btree or hash */
		if (op_form->amopmethod == BTREE_AM_OID ||
			op_form->amopmethod == HASH_AM_OID)
		{
			if (op_in_opfamily(opno2, op_form->amopfamily))
			{
				result = true;
				break;
			}
		}
	}

	ReleaseSysCacheList(catlist);

	return result;
}


/*				---------- AMPROC CACHES ----------						 */

/*
 * get_opfamily_proc
 *		Get the OID of the specified support function
 *		for the specified opfamily and datatypes.
 *
 * Returns InvalidOid if there is no pg_amproc entry for the given keys.
 */
Oid
get_opfamily_proc(Oid opfamily, Oid lefttype, Oid righttype, int16 procnum)
{
	HeapTuple	tp;
	Form_pg_amproc amproc_tup;
	RegProcedure result;

	tp = SearchSysCache4(AMPROCNUM,
						 ObjectIdGetDatum(opfamily),
						 ObjectIdGetDatum(lefttype),
						 ObjectIdGetDatum(righttype),
						 Int16GetDatum(procnum));
	if (!HeapTupleIsValid(tp))
		return InvalidOid;
	amproc_tup = (Form_pg_amproc) GETSTRUCT(tp);
	result = amproc_tup->amproc;
	ReleaseSysCache(tp);
	return result;
}


/*				---------- ATTRIBUTE CACHES ----------					 */

/*
 * get_attname
 *		Given the relation id and the attribute number,
 *		return the "attname" field from the attribute relation.
 *
 * Note: returns a palloc'd copy of the string, or NULL if no such attribute.
 */
char *
get_attname(Oid relid, AttrNumber attnum)
{
	HeapTuple	tp;

	tp = SearchSysCache2(ATTNUM,
						 ObjectIdGetDatum(relid),
						 Int16GetDatum(attnum));
	if (HeapTupleIsValid(tp))
	{
		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
		char	   *result;

		result = pstrdup(NameStr(att_tup->attname));
		ReleaseSysCache(tp);
		return result;
	}
	else
		return NULL;
}

/*
 * get_relid_attribute_name
 *
 * Same as above routine get_attname(), except that error
 * is handled by elog() instead of returning NULL.
 */
char *
get_relid_attribute_name(Oid relid, AttrNumber attnum)
{
	char	   *attname;

	attname = get_attname(relid, attnum);
	if (attname == NULL)
		elog(ERROR, "cache lookup failed for attribute %d of relation %u",
			 attnum, relid);
	return attname;
}

/*
 * get_attnum
 *
 *		Given the relation id and the attribute name,
 *		return the "attnum" field from the attribute relation.
 *
 *		Returns InvalidAttrNumber if the attr doesn't exist (or is dropped).
 */
AttrNumber
get_attnum(Oid relid, const char *attname)
{
	HeapTuple	tp;

	tp = SearchSysCacheAttName(relid, attname);
	if (HeapTupleIsValid(tp))
	{
		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
		AttrNumber	result;

		result = att_tup->attnum;
		ReleaseSysCache(tp);
		return result;
	}
	else
		return InvalidAttrNumber;
}

/*
 * get_atttype
 *
 *		Given the relation OID and the attribute number with the relation,
 *		return the attribute type OID.
 */
Oid
get_atttype(Oid relid, AttrNumber attnum)
{
	HeapTuple	tp;

	tp = SearchSysCache2(ATTNUM,
						 ObjectIdGetDatum(relid),
						 Int16GetDatum(attnum));
	if (HeapTupleIsValid(tp))
	{
		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
		Oid			result;

		result = att_tup->atttypid;
		ReleaseSysCache(tp);
		return result;
	}
	else
		return InvalidOid;
}

/*
 * get_atttypmod
 *
 *		Given the relation id and the attribute number,
 *		return the "atttypmod" field from the attribute relation.
 */
int32
get_atttypmod(Oid relid, AttrNumber attnum)
{
	HeapTuple	tp;

	tp = SearchSysCache2(ATTNUM,
						 ObjectIdGetDatum(relid),
						 Int16GetDatum(attnum));
	if (HeapTupleIsValid(tp))
	{
		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
		int32		result;

		result = att_tup->atttypmod;
		ReleaseSysCache(tp);
		return result;
	}
	else
		return -1;
}

/*
 * get_atttypetypmodcoll
 *
 *		A three-fer: given the relation id and the attribute number,
 *		fetch atttypid, atttypmod, and attcollation in a single cache lookup.
 *
 * Unlike the otherwise-similar get_atttype/get_atttypmod, this routine
 * raises an error if it can't obtain the information.
 */
void
get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
					  Oid *typid, int32 *typmod, Oid *collid)
{
	HeapTuple	tp;
	Form_pg_attribute att_tup;

	tp = SearchSysCache2(ATTNUM,
						 ObjectIdGetDatum(relid),
						 Int16GetDatum(attnum));
	if (!HeapTupleIsValid(tp))
		elog(ERROR, "cache lookup failed for attribute %d of relation %u",
			 attnum, relid);
	att_tup = (Form_pg_attribute) GETSTRUCT(tp);

	*typid = att_tup->atttypid;
	*typmod = att_tup->atttypmod;
	*collid = att_tup->attcollation;
	ReleaseSysCache(tp);
}

/*				---------- COLLATION CACHE ----------					 */

/*
 * get_collation_name
 *		Returns the name of a given pg_collation entry.
 *
 * Returns a palloc'd copy of the string, or NULL if no such constraint.
 *
 * NOTE: since collation name is not unique, be wary of code that uses this
 * for anything except preparing error messages.
 */
char *
get_collation_name(Oid colloid)
{
	HeapTuple	tp;

	tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(colloid));
	if (HeapTupleIsValid(tp))
	{
		Form_pg_collation colltup = (Form_pg_collation) GETSTRUCT(tp);
		char	   *result;

		result = pstrdup(NameStr(colltup->collname));
		ReleaseSysCache(tp);
		return result;
	}
	else
		return NULL;
}

/*				---------- CONSTRAINT CACHE ----------					 */

/*
 * get_constraint_name
 *		Returns the name of a given pg_constraint entry.
 *
 * Returns a palloc'd copy of the string, or NULL if no such constraint.
 *
 * NOTE: since constraint name is not unique, be wary of code that uses this
 * for anything except preparing error messages.
 */
char *
get_constraint_name(Oid conoid)
{
	HeapTuple	tp;

	tp = SearchSysCache1(CONSTROID, ObjectIdGetDatum(conoid));
	if (HeapTupleIsValid(tp))
	{
		Form_pg_constraint contup = (Form_pg_constraint) GETSTRUCT(tp);
		char	   *result;

		result = pstrdup(NameStr(contup->conname));
		ReleaseSysCache(tp);
		return result;
	}
	else
		return NULL;
}

/*				---------- OPCLASS CACHE ----------						 */

/*
 * get_opclass_family