1 files changed, 244 insertions, 0 deletions
diff --git a/src/backend/utils/cache/relfilenumbermap.c b/src/backend/utils/cache/relfilenumbermap.c
new file mode 100644
index 00000000000..c4245d5ccdd
--- /dev/null
+++ b/src/backend/utils/cache/relfilenumbermap.c
@@ -0,0 +1,244 @@
+/*-------------------------------------------------------------------------
+ *
+ * relfilenumbermap.c
+ *	  relfilenumber to oid mapping cache.
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/cache/relfilenumbermap.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/genam.h"
+#include "access/htup_details.h"
+#include "access/table.h"
+#include "catalog/pg_class.h"
+#include "catalog/pg_tablespace.h"
+#include "miscadmin.h"
+#include "utils/builtins.h"
+#include "utils/catcache.h"
+#include "utils/fmgroids.h"
+#include "utils/hsearch.h"
+#include "utils/inval.h"
+#include "utils/rel.h"
+#include "utils/relfilenumbermap.h"
+#include "utils/relmapper.h"
+
+/* Hash table for information about each relfilenumber <-> oid pair */
+static HTAB *RelfilenumberMapHash = NULL;
+
+/* built first time through in InitializeRelfilenumberMap */
+static ScanKeyData relfilenumber_skey[2];
+
+typedef struct
+{
+	Oid			reltablespace;
+	RelFileNumber relfilenumber;
+} RelfilenumberMapKey;
+
+typedef struct
+{
+	RelfilenumberMapKey key;	/* lookup key - must be first */
+	Oid			relid;			/* pg_class.oid */
+} RelfilenumberMapEntry;
+
+/*
+ * RelfilenumberMapInvalidateCallback
+ *		Flush mapping entries when pg_class is updated in a relevant fashion.
+ */
+static void
+RelfilenumberMapInvalidateCallback(Datum arg, Oid relid)
+{
+	HASH_SEQ_STATUS status;
+	RelfilenumberMapEntry *entry;
+
+	/* callback only gets registered after creating the hash */
+	Assert(RelfilenumberMapHash != NULL);
+
+	hash_seq_init(&status, RelfilenumberMapHash);
+	while ((entry = (RelfilenumberMapEntry *) hash_seq_search(&status)) != NULL)
+	{
+		/*
+		 * If relid is InvalidOid, signaling a complete reset, we must remove
+		 * all entries, otherwise just remove the specific relation's entry.
+		 * Always remove negative cache entries.
+		 */
+		if (relid == InvalidOid ||	/* complete reset */
+			entry->relid == InvalidOid ||	/* negative cache entry */
+			entry->relid == relid)	/* individual flushed relation */
+		{
+			if (hash_search(RelfilenumberMapHash,
+							(void *) &entry->key,
+							HASH_REMOVE,
+							NULL) == NULL)
+				elog(ERROR, "hash table corrupted");
+		}
+	}
+}
+
+/*
+ * InitializeRelfilenumberMap
+ *		Initialize cache, either on first use or after a reset.
+ */
+static void
+InitializeRelfilenumberMap(void)
+{
+	HASHCTL		ctl;
+	int			i;
+
+	/* Make sure we've initialized CacheMemoryContext. */
+	if (CacheMemoryContext == NULL)
+		CreateCacheMemoryContext();
+
+	/* build skey */
+	MemSet(&relfilenumber_skey, 0, sizeof(relfilenumber_skey));
+
+	for (i = 0; i < 2; i++)
+	{
+		fmgr_info_cxt(F_OIDEQ,
+					  &relfilenumber_skey[i].sk_func,
+					  CacheMemoryContext);
+		relfilenumber_skey[i].sk_strategy = BTEqualStrategyNumber;
+		relfilenumber_skey[i].sk_subtype = InvalidOid;
+		relfilenumber_skey[i].sk_collation = InvalidOid;
+	}
+
+	relfilenumber_skey[0].sk_attno = Anum_pg_class_reltablespace;
+	relfilenumber_skey[1].sk_attno = Anum_pg_class_relfilenode;
+
+	/*
+	 * Only create the RelfilenumberMapHash now, so we don't end up partially
+	 * initialized when fmgr_info_cxt() above ERRORs out with an out of memory
+	 * error.
+	 */
+	ctl.keysize = sizeof(RelfilenumberMapKey);
+	ctl.entrysize = sizeof(RelfilenumberMapEntry);
+	ctl.hcxt = CacheMemoryContext;
+
+	RelfilenumberMapHash =
+		hash_create("RelfilenumberMap cache", 64, &ctl,
+					HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	/* Watch for invalidation events. */
+	CacheRegisterRelcacheCallback(RelfilenumberMapInvalidateCallback,
+								  (Datum) 0);
+}
+
+/*
+ * Map a relation's (tablespace, relfilenumber) to a relation's oid and cache
+ * the result.
+ *
+ * Returns InvalidOid if no relation matching the criteria could be found.
+ */
+Oid
+RelidByRelfilenumber(Oid reltablespace, RelFileNumber relfilenumber)
+{
+	RelfilenumberMapKey key;
+	RelfilenumberMapEntry *entry;
+	bool		found;
+	SysScanDesc scandesc;
+	Relation	relation;
+	HeapTuple	ntp;
+	ScanKeyData skey[2];
+	Oid			relid;
+
+	if (RelfilenumberMapHash == NULL)
+		InitializeRelfilenumberMap();
+
+	/* 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.relfilenumber = relfilenumber;
+
+	/*
+	 * Check cache and return entry if one is 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 it's basically free.
+	 */
+	entry = hash_search(RelfilenumberMapHash, (void *) &key, HASH_FIND, &found);
+
+	if (found)
+		return entry->relid;
+
+	/* ok, no previous cache entry, do it the hard way */
+
+	/* initialize empty/negative cache entry before doing the actual lookups */
+	relid = InvalidOid;
+
+	if (reltablespace == GLOBALTABLESPACE_OID)
+	{
+		/*
+		 * Ok, shared table, check relmapper.
+		 */
+		relid = RelationMapFilenumberToOid(relfilenumber, true);
+	}
+	else
+	{
+		/*
+		 * Not a shared table, could either be a plain relation or a
+		 * non-shared, nailed one, like e.g. pg_class.
+		 */
+
+		/* check for plain relations by looking in pg_class */
+		relation = table_open(RelationRelationId, AccessShareLock);
+
+		/* copy scankey to local copy, it will be modified during the scan */
+		memcpy(skey, relfilenumber_skey, sizeof(skey));
+
+		/* set scan arguments */
+		skey[0].sk_argument = ObjectIdGetDatum(reltablespace);
+		skey[1].sk_argument = ObjectIdGetDatum(relfilenumber);
+
+		scandesc = systable_beginscan(relation,
+									  ClassTblspcRelfilenodeIndexId,
+									  true,
+									  NULL,
+									  2,
+									  skey);
+
+		found = false;
+
+		while (HeapTupleIsValid(ntp = systable_getnext(scandesc)))
+		{
+			Form_pg_class classform = (Form_pg_class) GETSTRUCT(ntp);
+
+			if (found)
+				elog(ERROR,
+					 "unexpected duplicate for tablespace %u, relfilenumber %u",
+					 reltablespace, relfilenumber);
+			found = true;
+
+			Assert(classform->reltablespace == reltablespace);
+			Assert(classform->relfilenode == relfilenumber);
+			relid = classform->oid;
+		}
+
+		systable_endscan(scandesc);
+		table_close(relation, AccessShareLock);
+
+		/* check for tables that are mapped but not shared */
+		if (!found)
+			relid = RelationMapFilenumberToOid(relfilenumber, false);
+	}
+
+	/*
+	 * Only enter entry into cache now, our opening of pg_class could have
+	 * caused cache invalidations to be executed which would have deleted a
+	 * new entry if we had entered it above.
+	 */
+	entry = hash_search(RelfilenumberMapHash, (void *) &key, HASH_ENTER, &found);
+	if (found)
+		elog(ERROR, "corrupted hashtable");
+	entry->relid = relid;
+
+	return relid;
+}