A session that does not have any live snapshots does not have to be waited for

when we are waiting for old snapshots to go away during a concurrent index
build.  In particular, this rule lets us avoid waiting for
idle-in-transaction sessions.

This logic could be improved further if we had some way to wake up when
the session we are currently waiting for goes idle-in-transaction.  However
that would be a significantly more complex/invasive patch, so it'll have to
wait for some other day.

Simon Riggs, with some improvements by Tom.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index 7ec3a24cb6e..e2b27ccb98b 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/lock.h,v 1.115 2009/01/01 17:24:01 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/lock.h,v 1.116 2009/04/04 17:40:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -67,6 +67,12 @@ typedef struct
 #define VirtualTransactionIdIsValid(vxid) \
 	(((vxid).backendId != InvalidBackendId) && \
 	 LocalTransactionIdIsValid((vxid).localTransactionId))
+#define VirtualTransactionIdEquals(vxid1, vxid2) \
+	((vxid1).backendId == (vxid2).backendId && \
+	 (vxid1).localTransactionId == (vxid2).localTransactionId)
+#define SetInvalidVirtualTransactionId(vxid) \
+	((vxid).backendId = InvalidBackendId, \
+	 (vxid).localTransactionId = InvalidLocalTransactionId)
 #define GET_VXID_FROM_PGPROC(vxid, proc) \
 	((vxid).backendId = (proc).backendId, \
 	 (vxid).localTransactionId = (proc).lxid)