1. xact.c: update comments about changing MyProc->xid and MyProc->xmin.

2. varsup.c:ReadNewTransactionId(): don't read nextXid from disk -
   this func doesn't allocate next xid, so ShmemVariableCache->nextXid
   may be used (but GetNewTransactionId() must be called first).
3. vacuum.c: change elog(ERROR, "Child item....") to elog(NOTICE) -
   this is not ERROR, proper handling is just not implemented, yet.
4. s_lock.c: increase S_MAX_BUSY by 2 times.
5. shmem.c:GetSnapshotData(): have to call ReadNewTransactionId()
   _after_ SpinAcquire(ShmemIndexLock).

src/backend/access/transam/varsup.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.21 1999/06/03 04:41:40 vadim Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/varsup.c,v 1.22 1999/06/06 20:19:33 vadim Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -335,16 +335,13 @@ ReadNewTransactionId(TransactionId *xid)
 
 	SpinAcquire(OidGenLockId);	/* not good for concurrency... */
 
-	if (ShmemVariableCache->xid_count == 0)
-	{
-		TransactionId nextid;
-
-		VariableRelationGetNextXid(&nextid);
-		TransactionIdStore(nextid, &(ShmemVariableCache->nextXid));
-		ShmemVariableCache->xid_count = VAR_XID_PREFETCH;
-		TransactionIdAdd(&nextid, VAR_XID_PREFETCH);
-		VariableRelationPutNextXid(nextid);
-	}
+	/*
+	 * Note that we don't check is ShmemVariableCache->xid_count equal
+	 * to 0 or not. This will work as long as we don't call 
+	 * ReadNewTransactionId() before GetNewTransactionId().
+	 */
+	if (ShmemVariableCache->nextXid == 0)
+		elog(ERROR, "ReadNewTransactionId: ShmemVariableCache->nextXid is not initialized");
 
 	TransactionIdStore(ShmemVariableCache->nextXid, xid);
 

src/backend/access/transam/xact.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.39 1999/06/03 13:33:12 vadim Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.40 1999/06/06 20:19:34 vadim Exp $
  *
  * NOTES
  *		Transaction aborts can now occur two ways:
@@ -942,15 +942,11 @@ CommitTransaction()
 	/*
 	 * Let others know about no transaction in progress by me.
 	 * Note that this must be done _before_ releasing locks we hold 
-	 * and SpinAcquire(ShmemIndexLock) is required - or bad (too high) 
-	 * XmaxRecent value might be used by vacuum: UPDATE with xid 0 is 
+	 * and SpinAcquire(ShmemIndexLock) is required: UPDATE with xid 0 is 
 	 * blocked by xid 1' UPDATE, xid 1 is doing commit while xid 2 
 	 * gets snapshot - if xid 2' GetSnapshotData sees xid 1 as running
-	 * then it must see xid 0 as running as well or XmaxRecent = 1
-	 * might be used by concurrent vacuum causing
-	 *         ERROR:  Child itemid marked as unused
-	 * This bug was reported by Hiroshi Inoue and I was able to reproduce
-	 * it with 3 sessions and gdb.	- vadim 06/03/99
+	 * then it must see xid 0 as running as well or it will see two
+	 * tuple versions - one deleted by xid 1 and one inserted by xid 0.
 	 */
 	if (MyProc != (PROC *) NULL)
 	{

src/backend/commands/vacuum.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.106 1999/06/03 13:25:54 vadim Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.107 1999/06/06 20:19:34 vadim Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1238,11 +1238,28 @@ vc_rpfheap(VRelStats *vacrelstats, Relation onerel,
 					Citemid = PageGetItemId(Cpage,
 									  ItemPointerGetOffsetNumber(&Ctid));
 					if (!ItemIdIsUsed(Citemid))
-						elog(ERROR, "Child itemid marked as unused");
+					{
+						/*
+						 * This means that in the middle of chain there was
+						 * tuple updated by older (than XmaxRecent) xaction
+						 * and this tuple is already deleted by me. Actually,
+						 * upper part of chain should be removed and seems 
+						 * that this should be handled in vc_scanheap(), but
+						 * it's not implemented at the moment and so we
+						 * just stop shrinking here.
+						 */
+						ReleaseBuffer(Cbuf);
+						pfree(vtmove);
+						vtmove = NULL;
+						elog(NOTICE, "Child itemid in update-chain marked as unused - can't continue vc_rpfheap");
+						break;
+					}
 					tp.t_data = (HeapTupleHeader) PageGetItem(Cpage, Citemid);
 					tp.t_self = Ctid;
 					tlen = tp.t_len = ItemIdGetLength(Citemid);
 				}
+				if (vtmove == NULL)
+					break;
 				/* first, can chain be moved ? */
 				for (;;)
 				{
@@ -1336,6 +1353,7 @@ vc_rpfheap(VRelStats *vacrelstats, Relation onerel,
 						Ptp.t_data = (HeapTupleHeader) PageGetItem(Ppage, Pitemid);
 						Assert(Ptp.t_data->t_xmax == tp.t_data->t_xmin);
 
+#ifdef NOT_USED			/* I'm not sure that this will wotk properly... */
 						/*
 						 * If this tuple is updated version of row and it
 						 * was created by the same transaction then no one
@@ -1353,6 +1371,7 @@ vc_rpfheap(VRelStats *vacrelstats, Relation onerel,
 							WriteBuffer(Pbuf);
 							continue;
 						}
+#endif
 						tp.t_data = Ptp.t_data;
 						tlen = tp.t_len = ItemIdGetLength(Pitemid);
 						if (freeCbuf)
@@ -1763,7 +1782,7 @@ Elapsed %u/%u sec.",
 			page = BufferGetPage(buf);
 			num_tuples = 0;
 			for (offnum = FirstOffsetNumber;
-				 offnum < maxoff;
+				 offnum <= maxoff;
 				 offnum = OffsetNumberNext(offnum))
 			{
 				itemid = PageGetItemId(page, offnum);

src/backend/storage/buffer/s_lock.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/Attic/s_lock.c,v 1.20 1999/05/25 22:04:32 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/buffer/Attic/s_lock.c,v 1.21 1999/06/06 20:19:35 vadim Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -28,7 +28,7 @@
  * note: total time to cycle through all 16 entries might be about .07 sec.
  */
 #define S_NSPINCYCLE	20
-#define S_MAX_BUSY		500 * S_NSPINCYCLE
+#define S_MAX_BUSY		1000 * S_NSPINCYCLE
 
 int			s_spincycle[S_NSPINCYCLE] =
 {0, 0, 0, 0, 10000, 0, 0, 0, 10000, 0,

src/backend/storage/ipc/shmem.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.41 1999/06/03 13:33:13 vadim Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.42 1999/06/06 20:19:35 vadim Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -652,9 +652,15 @@ GetSnapshotData(bool serializable)
 
 	snapshot->xip = (TransactionId *) malloc(have * sizeof(TransactionId));
 	snapshot->xmin = cid;
-	ReadNewTransactionId(&(snapshot->xmax));
 
 	SpinAcquire(ShmemIndexLock);
+	/*
+	 * Unfortunately, we have to call ReadNewTransactionId()
+	 * after acquiring ShmemIndexLock above. It's not good because of
+	 * ReadNewTransactionId() does SpinAcquire(OidGenLockId) but
+	 * _necessary_.
+	 */
+	ReadNewTransactionId(&(snapshot->xmax));
 
 	hash_seq((HTAB *) NULL);
 	while ((result = (ShmemIndexEnt *) hash_seq(ShmemIndex)) != NULL)