Solve the problem of OID collisions by probing for duplicate OIDs

whenever we generate a new OID.  This prevents occasional duplicate-OID
errors that can otherwise occur once the OID counter has wrapped around.
Duplicate relfilenode values are also checked for when creating new
physical files.  Per my recent proposal.

Author: tglsfdc

doc/src/sgml/ddl.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.42 2005/07/14 06:17:35 neilc Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/ddl.sgml,v 1.43 2005/08/12 01:35:53 tgl Exp $ -->
 
 <chapter id="ddl">
  <title>Data Definition</title>
@@ -871,7 +871,7 @@ CREATE TABLE order_items (
       The object identifier (object ID) of a row. This column is only
       present if the table was created using <literal>WITH
       OIDS</literal>, or if the <xref linkend="guc-default-with-oids">
-      configuration variable was enabled. This column is of type
+      configuration variable was set. This column is of type
       <type>oid</type> (same name as the column); see <xref
       linkend="datatype-oid"> for more information about the type.
      </para>
@@ -992,7 +992,13 @@ CREATE TABLE order_items (
      <listitem>
       <para>
        A unique constraint should be created on the OID column of each
-       table for which the OID will be used to identify rows.
+       table for which the OID will be used to identify rows.  When such
+       a unique constraint (or unique index) exists, the system takes
+       care not to generate an OID matching an already-existing row.
+       (Of course, this is only possible if the table contains fewer
+       than 2<superscript>32</> (4 billion) rows, and in practice the
+       table size had better be much less than that, or performance
+       may suffer.)
       </para>
      </listitem>
      <listitem>
@@ -1005,9 +1011,8 @@ CREATE TABLE order_items (
      <listitem>
       <para>
        The tables in question should be created using <literal>WITH
-       OIDS</literal> to ensure forward compatibility with future
-       releases of <productname>PostgreSQL</productname>.  It is
-       planned that <literal>WITHOUT OIDS</> will become the default.
+       OIDS</literal>.  As of <productname>PostgreSQL</productname> 8.1,
+       <literal>WITHOUT OIDS</> is the default.
       </para>
      </listitem>
     </itemizedlist>

src/backend/access/heap/heapam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.196 2005/08/01 20:31:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.197 2005/08/12 01:35:54 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1069,9 +1069,7 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 		 * pointers to one another).
 		 */
 		if (!OidIsValid(HeapTupleGetOid(tup)))
-			HeapTupleSetOid(tup, newoid());
-		else
-			CheckMaxObjectId(HeapTupleGetOid(tup));
+			HeapTupleSetOid(tup, GetNewOid(relation));
 	}
 	else
 	{

src/backend/access/heap/tuptoaster.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.51 2005/08/02 16:11:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.52 2005/08/12 01:35:54 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1006,6 +1006,15 @@ toast_save_datum(Relation rel, Datum value)
 	char	   *data_p;
 	int32		data_todo;
 
+	/*
+	 * Open the toast relation and its index.  We can use the index to
+	 * check uniqueness of the OID we assign to the toasted item, even
+	 * though it has additional columns besides OID.
+	 */
+	toastrel = heap_open(rel->rd_rel->reltoastrelid, RowExclusiveLock);
+	toasttupDesc = toastrel->rd_att;
+	toastidx = index_open(toastrel->rd_rel->reltoastidxid);
+
 	/*
 	 * Create the varattrib reference
 	 */
@@ -1023,7 +1032,8 @@ toast_save_datum(Relation rel, Datum value)
 
 	result->va_content.va_external.va_extsize =
 		VARATT_SIZE(value) - VARHDRSZ;
-	result->va_content.va_external.va_valueid = newoid();
+	result->va_content.va_external.va_valueid =
+		GetNewOidWithIndex(toastrel, toastidx);
 	result->va_content.va_external.va_toastrelid =
 		rel->rd_rel->reltoastrelid;
 
@@ -1043,12 +1053,9 @@ toast_save_datum(Relation rel, Datum value)
 	data_todo = VARATT_SIZE(value) - VARHDRSZ;
 
 	/*
-	 * Open the toast relation.  We must explicitly lock the toast index
-	 * because we aren't using an index scan here.
+	 * We must explicitly lock the toast index because we aren't using an
+	 * index scan here.
 	 */
-	toastrel = heap_open(rel->rd_rel->reltoastrelid, RowExclusiveLock);
-	toasttupDesc = toastrel->rd_att;
-	toastidx = index_open(toastrel->rd_rel->reltoastidxid);
 	LockRelation(toastidx, RowExclusiveLock);
 
 	/*

src/backend/access/transam/varsup.c

@@ -6,7 +6,7 @@
  * Copyright (c) 2000-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/varsup.c,v 1.64 2005/05/19 21:35:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/varsup.c,v 1.65 2005/08/12 01:35:55 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -247,13 +247,16 @@ SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
 }
 
 
-/* ----------------------------------------------------------------
- *					object id generation support
- * ----------------------------------------------------------------
+/*
+ * GetNewObjectId -- allocate a new OID
+ *
+ * OIDs are generated by a cluster-wide counter.  Since they are only 32 bits
+ * wide, counter wraparound will occur eventually, and therefore it is unwise
+ * to assume they are unique unless precautions are taken to make them so.
+ * Hence, this routine should generally not be used directly.  The only
+ * direct callers should be GetNewOid() and GetNewRelFileNode() in
+ * catalog/catalog.c.
  */
-
-static Oid	lastSeenOid = InvalidOid;
-
 Oid
 GetNewObjectId(void)
 {
@@ -265,8 +268,9 @@ GetNewObjectId(void)
 	 * Check for wraparound of the OID counter.  We *must* not return 0
 	 * (InvalidOid); and as long as we have to check that, it seems a good
 	 * idea to skip over everything below FirstNormalObjectId too. (This
-	 * basically just reduces the odds of OID collision right after a wrap
-	 * occurs.)  Note we are relying on unsigned comparison here.
+	 * basically just avoids lots of collisions with bootstrap-assigned OIDs
+	 * right after a wrap occurs, so as to avoid a possibly large number of
+	 * iterations in GetNewOid.)  Note we are relying on unsigned comparison.
 	 *
 	 * During initdb, we start the OID generator at FirstBootstrapObjectId,
 	 * so we only enforce wrapping to that point when in bootstrap or
@@ -310,46 +314,5 @@ GetNewObjectId(void)
 
 	LWLockRelease(OidGenLock);
 
-	lastSeenOid = result;
-
 	return result;
 }
-
-void
-CheckMaxObjectId(Oid assigned_oid)
-{
-	if (lastSeenOid != InvalidOid && assigned_oid < lastSeenOid)
-		return;
-
-	LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
-
-	if (assigned_oid < ShmemVariableCache->nextOid)
-	{
-		lastSeenOid = ShmemVariableCache->nextOid - 1;
-		LWLockRelease(OidGenLock);
-		return;
-	}
-
-	/* If we are in the logged oid range, just bump nextOid up */
-	if (assigned_oid <= ShmemVariableCache->nextOid +
-		ShmemVariableCache->oidCount - 1)
-	{
-		ShmemVariableCache->oidCount -=
-			assigned_oid - ShmemVariableCache->nextOid + 1;
-		ShmemVariableCache->nextOid = assigned_oid + 1;
-		LWLockRelease(OidGenLock);
-		return;
-	}
-
-	/*
-	 * We have exceeded the logged oid range. We should lock the database
-	 * and kill all other backends but we are loading oid's that we can
-	 * not guarantee are unique anyway, so we must rely on the user.
-	 */
-
-	XLogPutNextOid(assigned_oid + VAR_OID_PREFETCH);
-	ShmemVariableCache->nextOid = assigned_oid + 1;
-	ShmemVariableCache->oidCount = VAR_OID_PREFETCH - 1;
-
-	LWLockRelease(OidGenLock);
-}