typcache.c

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/*-------------------------------------------------------------------------
 *
 * typcache.c
 *	  POSTGRES type cache code
 *
 * The type cache exists to speed lookup of certain information about data
 * types that is not directly available from a type's pg_type row.  In
 * particular, we use a type's default btree opclass, or the default hash
 * opclass if no btree opclass exists, to determine which operators should
 * be used for grouping and sorting the type (GROUP BY, ORDER BY ASC/DESC).
 *
 * Several seemingly-odd choices have been made to support use of the type
 * cache by the generic array comparison routines array_eq() and array_cmp().
 * Because these routines are used as index support operations, they cannot
 * leak memory.  To allow them to execute efficiently, all information that
 * either of them would like to re-use across calls is made available in the
 * type cache.
 *
 * Once created, a type cache entry lives as long as the backend does, so
 * there is no need for a call to release a cache entry.  (For present uses,
 * it would be okay to flush type cache entries at the ends of transactions,
 * if we needed to reclaim space.)
 *
 * There is presently no provision for clearing out a cache entry if the
 * stored data becomes obsolete.  (The code will work if a type acquires
 * opclasses it didn't have before while a backend runs --- but not if the
 * definition of an existing opclass is altered.)  However, the relcache
 * doesn't cope with opclasses changing under it, either, so this seems
 * a low-priority problem.
 *
 * We do support clearing the tuple descriptor part of a rowtype's cache
 * entry, since that may need to change as a consequence of ALTER TABLE.
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/cache/typcache.c,v 1.27 2008/01/01 19:45:53 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/hash.h"
#include "access/heapam.h"
#include "access/nbtree.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
#include "utils/typcache.h"


/* The main type cache hashtable searched by lookup_type_cache */
static HTAB *TypeCacheHash = NULL;

/*
 * We use a separate table for storing the definitions of non-anonymous
 * record types.  Once defined, a record type will be remembered for the
 * life of the backend.  Subsequent uses of the "same" record type (where
 * sameness means equalTupleDescs) will refer to the existing table entry.
 *
 * Stored record types are remembered in a linear array of TupleDescs,
 * which can be indexed quickly with the assigned typmod.  There is also
 * a hash table to speed searches for matching TupleDescs.	The hash key
 * uses just the first N columns' type OIDs, and so we may have multiple
 * entries with the same hash key.
 */
#define REC_HASH_KEYS	16		/* use this many columns in hash key */

typedef struct RecordCacheEntry
{
	/* the hash lookup key MUST BE FIRST */
	Oid			hashkey[REC_HASH_KEYS]; /* column type IDs, zero-filled */

	/* list of TupleDescs for record types with this hashkey */
	List	   *tupdescs;
} RecordCacheEntry;

static HTAB *RecordCacheHash = NULL;

static TupleDesc *RecordCacheArray = NULL;
static int32 RecordCacheArrayLen = 0;	/* allocated length of array */
static int32 NextRecordTypmod = 0;		/* number of entries used */


/*
 * lookup_type_cache
 *
 * Fetch the type cache entry for the specified datatype, and make sure that
 * all the fields requested by bits in 'flags' are valid.
 *
 * The result is never NULL --- we will elog() if the passed type OID is
 * invalid.  Note however that we may fail to find one or more of the
 * requested opclass-dependent fields; the caller needs to check whether
 * the fields are InvalidOid or not.
 */
TypeCacheEntry *
lookup_type_cache(Oid type_id, int flags)
{
	TypeCacheEntry *typentry;
	bool		found;

	if (TypeCacheHash == NULL)
	{
		/* First time through: initialize the hash table */
		HASHCTL		ctl;

		if (!CacheMemoryContext)
			CreateCacheMemoryContext();

		MemSet(&ctl, 0, sizeof(ctl));
		ctl.keysize = sizeof(Oid);
		ctl.entrysize = sizeof(TypeCacheEntry);
		ctl.hash = oid_hash;
		TypeCacheHash = hash_create("Type information cache", 64,
									&ctl, HASH_ELEM | HASH_FUNCTION);
	}

	/* Try to look up an existing entry */
	typentry = (TypeCacheEntry *) hash_search(TypeCacheHash,
											  (void *) &type_id,
											  HASH_FIND, NULL);
	if (typentry == NULL)
	{
		/*
		 * If we didn't find one, we want to make one.  But first look up the
		 * pg_type row, just to make sure we don't make a cache entry for an
		 * invalid type OID.
		 */
		HeapTuple	tp;
		Form_pg_type typtup;

		tp = SearchSysCache(TYPEOID,
							ObjectIdGetDatum(type_id),
							0, 0, 0);
		if (!HeapTupleIsValid(tp))
			elog(ERROR, "cache lookup failed for type %u", type_id);
		typtup = (Form_pg_type) GETSTRUCT(tp);
		if (!typtup->typisdefined)
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_OBJECT),
					 errmsg("type \"%s\" is only a shell",
							NameStr(typtup->typname))));

		/* Now make the typcache entry */
		typentry = (TypeCacheEntry *) hash_search(TypeCacheHash,
												  (void *) &type_id,
												  HASH_ENTER, &found);
		Assert(!found);			/* it wasn't there a moment ago */

		MemSet(typentry, 0, sizeof(TypeCacheEntry));
		typentry->type_id = type_id;
		typentry->typlen = typtup->typlen;
		typentry->typbyval = typtup->typbyval;
		typentry->typalign = typtup->typalign;
		typentry->typtype = typtup->typtype;
		typentry->typrelid = typtup->typrelid;

		ReleaseSysCache(tp);
	}

	/* If we haven't already found the opclass, try to do so */
	if ((flags & (TYPECACHE_EQ_OPR | TYPECACHE_LT_OPR | TYPECACHE_GT_OPR |
				  TYPECACHE_CMP_PROC |
				  TYPECACHE_EQ_OPR_FINFO | TYPECACHE_CMP_PROC_FINFO |
				  TYPECACHE_BTREE_OPFAMILY)) &&
		typentry->btree_opf == InvalidOid)
	{
		Oid			opclass;

		opclass = GetDefaultOpClass(type_id, BTREE_AM_OID);
		if (OidIsValid(opclass))
		{
			typentry->btree_opf = get_opclass_family(opclass);
			typentry->btree_opintype = get_opclass_input_type(opclass);
		}
		/* Only care about hash opclass if no btree opclass... */
		if (typentry->btree_opf == InvalidOid)
		{
			if (typentry->hash_opf == InvalidOid)
			{
				opclass = GetDefaultOpClass(type_id, HASH_AM_OID);
				if (OidIsValid(opclass))
				{
					typentry->hash_opf = get_opclass_family(opclass);
					typentry->hash_opintype = get_opclass_input_type(opclass);
				}
			}
		}
		else
		{
			/*
			 * If we find a btree opclass where previously we only found a
			 * hash opclass, forget the hash equality operator so we can use
			 * the btree operator instead.
			 */
			typentry->eq_opr = InvalidOid;
			typentry->eq_opr_finfo.fn_oid = InvalidOid;
		}
	}

	/* Look for requested operators and functions */
	if ((flags & (TYPECACHE_EQ_OPR | TYPECACHE_EQ_OPR_FINFO)) &&
		typentry->eq_opr == InvalidOid)
	{
		if (typentry->btree_opf != InvalidOid)
			typentry->eq_opr = get_opfamily_member(typentry->btree_opf,
												   typentry->btree_opintype,
												   typentry->btree_opintype,
												   BTEqualStrategyNumber);
		if (typentry->eq_opr == InvalidOid &&
			typentry->hash_opf != InvalidOid)
			typentry->eq_opr = get_opfamily_member(typentry->hash_opf,
												   typentry->hash_opintype,
												   typentry->hash_opintype,
												   HTEqualStrategyNumber);
	}
	if ((flags & TYPECACHE_LT_OPR) && typentry->lt_opr == InvalidOid)
	{
		if (typentry->btree_opf != InvalidOid)
			typentry->lt_opr = get_opfamily_member(typentry->btree_opf,
												   typentry->btree_opintype,
												   typentry->btree_opintype,
												   BTLessStrategyNumber);
	}
	if ((flags & TYPECACHE_GT_OPR) && typentry->gt_opr == InvalidOid)
	{
		if (typentry->btree_opf != InvalidOid)
			typentry->gt_opr = get_opfamily_member(typentry->btree_opf,
												   typentry->btree_opintype,
												   typentry->btree_opintype,
												   BTGreaterStrategyNumber);
	}
	if ((flags & (TYPECACHE_CMP_PROC | TYPECACHE_CMP_PROC_FINFO)) &&
		typentry->cmp_proc == InvalidOid)
	{
		if (typentry->btree_opf != InvalidOid)
			typentry->cmp_proc = get_opfamily_proc(typentry->btree_opf,
												   typentry->btree_opintype,
												   typentry->btree_opintype,
												   BTORDER_PROC);
	}

	/*
	 * Set up fmgr lookup info as requested
	 *
	 * Note: we tell fmgr the finfo structures live in CacheMemoryContext,
	 * which is not quite right (they're really in DynaHashContext) but this
	 * will do for our purposes.
	 */
	if ((flags & TYPECACHE_EQ_OPR_FINFO) &&
		typentry->eq_opr_finfo.fn_oid == InvalidOid &&
		typentry->eq_opr != InvalidOid)
	{
		Oid			eq_opr_func;

		eq_opr_func = get_opcode(typentry->eq_opr);
		if (eq_opr_func != InvalidOid)
			fmgr_info_cxt(eq_opr_func, &typentry->eq_opr_finfo,
						  CacheMemoryContext);
	}
	if ((flags & TYPECACHE_CMP_PROC_FINFO) &&
		typentry->cmp_proc_finfo.fn_oid == InvalidOid &&