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

4 files changed, 13 insertions, 7 deletions

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 00f833d210e..40d4e9c35e6 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1984,7 +1984,7 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>relfilenode</structfield> <type>oid</type>
+       <structfield>relfilenode</structfield> <type>int8</type>
       </para>
       <para>
        Name of the on-disk file of this relation; zero means this
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 546213fa931..d8718ed61e6 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25210,6 +25210,11 @@ SELECT collation for ('foo' COLLATE "de_DE");
        <entry><type>timestamp with time zone</type></entry>
       </row>
 
+      <row>
+       <entry><structfield>next_relfilenumber</structfield></entry>
+       <entry><type>timestamp with time zone</type></entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml
index a06fd3e26de..e2222655804 100644
--- a/doc/src/sgml/pgbuffercache.sgml
+++ b/doc/src/sgml/pgbuffercache.sgml
@@ -62,7 +62,7 @@
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>relfilenode</structfield> <type>oid</type>
+       <structfield>relfilenode</structfield> <type>int8</type>
        (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>relfilenode</structfield>)
       </para>
       <para>
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index e5b9f3f1ffa..d9e9b0f43ee 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -217,11 +217,12 @@ with the suffix <literal>_init</literal> (see <xref linkend="storage-init"/>).
 
 <caution>
 <para>
-Note that while a table's filenode often matches its OID, this is
-<emphasis>not</emphasis> necessarily the case; some operations, like
-<command>TRUNCATE</command>, <command>REINDEX</command>, <command>CLUSTER</command> and some forms
-of <command>ALTER TABLE</command>, can change the filenode while preserving the OID.
-Avoid assuming that filenode and table OID are the same.
+Note that a table's filenode will normally be different than the OID. For
+system tables, the initial filenode will be equal to the table OID, but it will
+be different if the table has ever been subjected to a rewriting operation,
+such as <command>TRUNCATE</command>, <command>REINDEX</command>,
+<command>CLUSTER</command> or some forms of <command>ALTER TABLE</command>.
+For user tables, even the initial filenode will be different than the table OID.
 Also, for certain system catalogs including <structname>pg_class</structname> itself,
 <structname>pg_class</structname>.<structfield>relfilenode</structfield> contains zero.  The
 actual filenode number of these catalogs is stored in a lower-level data