Increase width of RelFileNumbers from 32 bits to 56 bits.

RelFileNumbers are now assigned using a separate counter, instead of
being assigned from the OID counter. This counter never wraps around:
if all 2^56 possible RelFileNumbers are used, an internal error
occurs. As the cluster is limited to 2^64 total bytes of WAL, this
limitation should not cause a problem in practice.

If the counter were 64 bits wide rather than 56 bits wide, we would
need to increase the width of the BufferTag, which might adversely
impact buffer lookup performance. Also, this lets us use bigint for
pg_class.relfilenode and other places where these values are exposed
at the SQL level without worrying about overflow.

This should remove the need to keep "tombstone" files around until
the next checkpoint when relations are removed. We do that to keep
RelFileNumbers from being recycled, but now that won't happen
anyway. However, this patch doesn't actually change anything in
this area; it just makes it possible for a future patch to do so.

Dilip Kumar, based on an idea from Andres Freund, who also reviewed
some earlier versions of the patch. Further review and some
wordsmithing by me. Also reviewed at various points by Ashutosh
Sharma, Vignesh C, Amul Sul, Álvaro Herrera, and Tom Lane.

Discussion: http://postgr.es/m/CA+Tgmobp7+7kmi4gkq7Y+4AM9fTvL+O1oQ4-5gFTT+6Ng-dQ=g@mail.gmail.com

1 files changed, 8 insertions, 8 deletions

diff --git a/src/include/catalog/pg_class.h b/src/include/catalog/pg_class.h
index e1f4eefa22..4768e5ebda 100644
--- a/src/include/catalog/pg_class.h
+++ b/src/include/catalog/pg_class.h
@@ -34,6 +34,13 @@ CATALOG(pg_class,1259,RelationRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(83,Relat
 	/* oid */
 	Oid			oid;
 
+	/* access method; 0 if not a table / index */
+	Oid			relam BKI_DEFAULT(heap) BKI_LOOKUP_OPT(pg_am);
+
+	/* identifier of physical storage file */
+	/* relfilenode == 0 means it is a "mapped" relation, see relmapper.c */
+	int64		relfilenode BKI_DEFAULT(0);
+
 	/* class name */
 	NameData	relname;
 
@@ -49,13 +56,6 @@ CATALOG(pg_class,1259,RelationRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(83,Relat
 	/* class owner */
 	Oid			relowner BKI_DEFAULT(POSTGRES) BKI_LOOKUP(pg_authid);
 
-	/* access method; 0 if not a table / index */
-	Oid			relam BKI_DEFAULT(heap) BKI_LOOKUP_OPT(pg_am);
-
-	/* identifier of physical storage file */
-	/* relfilenode == 0 means it is a "mapped" relation, see relmapper.c */
-	Oid			relfilenode BKI_DEFAULT(0);
-
 	/* identifier of table space for relation (0 means default for database) */
 	Oid			reltablespace BKI_DEFAULT(0) BKI_LOOKUP_OPT(pg_tablespace);
 
@@ -154,7 +154,7 @@ typedef FormData_pg_class *Form_pg_class;
 
 DECLARE_UNIQUE_INDEX_PKEY(pg_class_oid_index, 2662, ClassOidIndexId, on pg_class using btree(oid oid_ops));
 DECLARE_UNIQUE_INDEX(pg_class_relname_nsp_index, 2663, ClassNameNspIndexId, on pg_class using btree(relname name_ops, relnamespace oid_ops));
-DECLARE_INDEX(pg_class_tblspc_relfilenode_index, 3455, ClassTblspcRelfilenodeIndexId, on pg_class using btree(reltablespace oid_ops, relfilenode oid_ops));
+DECLARE_INDEX(pg_class_tblspc_relfilenode_index, 3455, ClassTblspcRelfilenodeIndexId, on pg_class using btree(reltablespace oid_ops, relfilenode int8_ops));
 
 #ifdef EXPOSE_TO_CLIENT_CODE