Improve confusing comment for HeapTupleSatisfiesNow, per gripe from Greg Stark.

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 5a19e12553d4b31a0cf76b9c8ac5975848297200..a3b52fa7eb436986aa25a5314590a4533a03c2ff 100644 (file)
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -32,7 +32,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.96 2006/09/03 15:59:39 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.97 2006/09/15 16:39:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -253,19 +253,18 @@ HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
  *
  * The satisfaction of "now" requires the following:
  *
- * ((Xmin == my-transaction &&             changed by the current transaction
- *  Cmin != my-command &&                  but not by this command, and
- *     (Xmax is null ||                        the row has not been deleted, or
- *         (Xmax == my-transaction &&          it was deleted by the current transaction
- *          Cmax != my-command)))              but not by this command,
+ * ((Xmin == my-transaction &&             inserted by the current transaction
+ *  Cmin < my-command &&                   before this command, and
+ *  (Xmax is null ||                       the row has not been deleted, or
+ *   (Xmax == my-transaction &&            it was deleted by the current transaction
+ *    Cmax >= my-command)))                but not before this command,
  * ||                                      or
- *
- * (Xmin is committed &&                   the row was modified by a committed transaction, and
+ * (Xmin is committed &&                   the row was inserted by a committed transaction, and
  *     (Xmax is null ||                    the row has not been deleted, or
- *         (Xmax == my-transaction &&          the row is being deleted by this command, or
- *          Cmax == my-command) ||
- *         (Xmax is not committed &&           the row was deleted by another transaction
- *          Xmax != my-transaction))))         that has not been committed
+ *      (Xmax == my-transaction &&         the row is being deleted by this transaction
+ *       Cmax >= my-command) ||            but it's not deleted "yet", or
+ *      (Xmax != my-transaction &&         the row was deleted by another transaction
+ *       Xmax is not committed))))         that has not been committed
  *
  *     mao says 17 march 1993:  the tests in this routine are correct;
  *     if you think they're not, you're wrong, and you should think