/*-------------------------------------------------------------------------
 *
 * relfilenodemap.c
 *	  relfilenode to oid mapping cache.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  src/backend/utils/cache/relfilenode.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/htup_details.h"
#include "catalog/indexing.h"
#include "catalog/pg_class.h"
#include "catalog/pg_tablespace.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/catcache.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"
#include "utils/relfilenodemap.h"
#include "utils/relmapper.h"

/* Hash table for informations about each relfilenode <-> oid pair */
static HTAB *RelfilenodeMapHash = NULL;

/* built first time through in InitializeRelfilenodeMap */
ScanKeyData relfilenode_skey[2];

typedef struct
{
	Oid			reltablespace;
	Oid			relfilenode;
} RelfilenodeMapKey;

typedef struct
{
	RelfilenodeMapKey key;	/* lookup key - must be first */
	Oid			relid;			/* pg_class.oid */
} RelfilenodeMapEntry;

/*
 * RelfilenodeMapInvalidateCallback
 *		Flush mapping entries when pg_class is updated in a relevant fashion.
 */
static void
RelfilenodeMapInvalidateCallback(Datum arg, Oid relid)
{
	HASH_SEQ_STATUS status;
	RelfilenodeMapEntry *entry;

	/* nothing to do if not active or deleted */
	if (RelfilenodeMapHash == NULL)
		return;

	/* if relid is InvalidOid, we must invalidate the entire cache */
	if (relid == InvalidOid)
	{
		hash_destroy(RelfilenodeMapHash);
		RelfilenodeMapHash = NULL;
		return;
	}

	hash_seq_init(&status, RelfilenodeMapHash);
	while ((entry = (RelfilenodeMapEntry *) hash_seq_search(&status)) != NULL)
	{
		/* Same OID may occur in more than one tablespace. */
		if (entry->relid == relid)
		{
			if (hash_search(RelfilenodeMapHash,
							(void *) &entry->key,
							HASH_REMOVE,
							NULL) == NULL)
				elog(ERROR, "hash table corrupted");
		}
	}
}

/*
 * RelfilenodeMapInvalidateCallback
 *		Initialize cache, either on first use or after a reset.
 */
static void
InitializeRelfilenodeMap(void)
{
	HASHCTL		ctl;
	static bool	initial_init_done = false;
	int i;

	/* Make sure we've initialized CacheMemoryContext. */
	if (CacheMemoryContext == NULL)
		CreateCacheMemoryContext();

	/* Initialize the hash table. */
	MemSet(&ctl, 0, sizeof(ctl));
	ctl.keysize = sizeof(RelfilenodeMapKey);
	ctl.entrysize = sizeof(RelfilenodeMapEntry);
	ctl.hash = tag_hash;
	ctl.hcxt = CacheMemoryContext;

	RelfilenodeMapHash =
		hash_create("RelfilenodeMap cache", 1024, &ctl,
					HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);

	/*
	 * For complete resets we simply delete the entire hash, but there's no
	 * need to do the other stuff multiple times. Especially the initialization
	 * of the relcche invalidation should only be done once.
	 */
	if (initial_init_done)
		return;

	/* build skey */
	MemSet(&relfilenode_skey, 0, sizeof(relfilenode_skey));

	for (i = 0; i < 2; i++)
	{
		fmgr_info_cxt(F_OIDEQ,
					  &relfilenode_skey[i].sk_func,
					  CacheMemoryContext);
		relfilenode_skey[i].sk_strategy = BTEqualStrategyNumber;
		relfilenode_skey[i].sk_subtype = InvalidOid;
		relfilenode_skey[i].sk_collation = InvalidOid;
	}

	relfilenode_skey[0].sk_attno = Anum_pg_class_reltablespace;
	relfilenode_skey[1].sk_attno = Anum_pg_class_relfilenode;

	/* Watch for invalidation events. */
	CacheRegisterRelcacheCallback(RelfilenodeMapInvalidateCallback,
								  (Datum) 0);
	initial_init_done = true;
}

/*
 * Map a relation's (tablespace, filenode) to a relation's oid and cache the
 * result.
 *
 * Returns InvalidOid if no relation matching the criteria could be found.
 */
Oid
RelidByRelfilenode(Oid reltablespace, Oid relfilenode)
{
	RelfilenodeMapKey key;
	RelfilenodeMapEntry *entry;
	bool found;
	SysScanDesc scandesc;
	Relation relation;
	HeapTuple ntp;
	ScanKeyData skey[2];

	if (RelfilenodeMapHash == NULL)
		InitializeRelfilenodeMap();

	/* pg_class will show 0 when the value is actually MyDatabaseTableSpace */
	if (reltablespace == MyDatabaseTableSpace)
		reltablespace = 0;

	MemSet(&key, 0, sizeof(key));
	key.reltablespace = reltablespace;
	key.relfilenode = relfilenode;

	/*
	 * Check cache and enter entry if nothing could be found. Even if no target
	 * relation can be found later on we store the negative match and return a
	 * InvalidOid from cache. That's not really necessary for performance since
	 * querying invalid values isn't supposed to be a frequent thing, but the
	 * implementation is simpler this way.
	 */
	entry = hash_search(RelfilenodeMapHash, (void *) &key, HASH_ENTER, &found);

	if (found)
		return entry->relid;

	/* initialize empty/negative cache entry before doing the actual lookup */
	entry->relid = InvalidOid;

	/* ok, no previous cache entry, do it the hard way */

	/* check shared tables */
	if (reltablespace == GLOBALTABLESPACE_OID)
	{
		entry->relid = RelationMapFilenodeToOid(relfilenode, true);
		return entry->relid;
	}

	/* check plain relations by looking in pg_class */
	relation = heap_open(RelationRelationId, AccessShareLock);

	/* copy scankey to local copy, it will be modified during the scan */
	memcpy(skey, relfilenode_skey, sizeof(skey));

	/* set scan arguments */
	skey[0].sk_argument = ObjectIdGetDatum(reltablespace);
	skey[1].sk_argument = ObjectIdGetDatum(relfilenode);

	scandesc = systable_beginscan(relation,
								  ClassTblspcRelfilenodeIndexId,
								  true,
								  NULL,
								  2,
								  skey);

	found = false;

	while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
	{
		bool isnull PG_USED_FOR_ASSERTS_ONLY;

		if (found)
			elog(ERROR,
				 "unexpected duplicate for tablespace %u, relfilenode %u",
				 reltablespace, relfilenode);
		found = true;

#ifdef USE_ASSERT_CHECKING
		if (assert_enabled)
		{
			Oid check;
			check = fastgetattr(ntp, Anum_pg_class_reltablespace,
								RelationGetDescr(relation),
								&isnull);
			Assert(!isnull && check == reltablespace);

			check = fastgetattr(ntp, Anum_pg_class_relfilenode,
								RelationGetDescr(relation),
								&isnull);
			Assert(!isnull && check == relfilenode);
		}
#endif
		entry->relid = HeapTupleGetOid(ntp);
	}

	systable_endscan(scandesc);
	heap_close(relation, AccessShareLock);

	/* check for tables that are mapped but not shared */
	if (!found)
		entry->relid = RelationMapFilenodeToOid(relfilenode, false);

	return entry->relid;
}