Truncate subtrans after each restartpoint.

Issue reported by Harald Kolb, patch by Fujii Masao, review by me.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index e9fc05c8ea713cb6e46e214e14ea7df9ea9ebb64..6249e3c724cffef5cc207118666d721d35e3df7f 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.430.2.2 2010/08/26 19:24:40 alvherre Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.430.2.3 2010/08/30 15:21:18 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -7706,10 +7706,14 @@ CreateRestartPoint(int flags)
    }
 
    /*
-    * Currently, there is no need to truncate pg_subtrans during recovery. If
-    * we did do that, we will need to have called StartupSUBTRANS() already
-    * and then TruncateSUBTRANS() would go here.
+    * Truncate pg_subtrans if possible.  We can throw away all data before
+    * the oldest XMIN of any running transaction.  No future transaction will
+    * attempt to reference any pg_subtrans entry older than that (see Asserts
+    * in subtrans.c).  When hot standby is disabled, though, we mustn't do
+    * this because StartupSUBTRANS hasn't been called yet.
     */
+   if (EnableHotStandby)
+       TruncateSUBTRANS(GetOldestXmin(true, false));
 
    /* All real work is done, but log before releasing lock. */
    if (log_checkpoints)