Improve tuplestore.c to support multiple concurrent read positions.

This facility replaces the former mark/restore support but is otherwise
upward-compatible with previous uses.  It's expected to be needed for
single evaluation of CTEs and also for window functions, so I'm committing
it separately instead of waiting for either one of those patches to be
finished.  Per discussion with Greg Stark and Hitoshi Harada.

Note: I removed nodeFunctionscan's mark/restore support, instead of bothering
to update it for this change, because it was dead code anyway.

1 files changed, 12 insertions, 5 deletions

diff --git a/src/include/utils/tuplestore.h b/src/include/utils/tuplestore.h
index 37f99fea3bd..3fe32f682b1 100644
--- a/src/include/utils/tuplestore.h
+++ b/src/include/utils/tuplestore.h
@@ -11,6 +11,8 @@
  * before it has all been written.	This is particularly useful for cursors,
  * because it allows random access within the already-scanned portion of
  * a query without having to process the underlying scan to completion.
+ * Also, it is possible to support multiple independent read pointers.
+ *
  * A temporary file is used to handle the data if it exceeds the
  * space limit specified by the caller.
  *
@@ -22,7 +24,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/utils/tuplestore.h,v 1.23 2008/03/25 19:26:53 neilc Exp $
+ * $PostgreSQL: pgsql/src/include/utils/tuplestore.h,v 1.24 2008/10/01 19:51:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -57,16 +59,21 @@ extern void tuplestore_putvalues(Tuplestorestate *state, TupleDesc tdesc,
 /* tuplestore_donestoring() used to be required, but is no longer used */
 #define tuplestore_donestoring(state)	((void) 0)
 
+extern int	tuplestore_alloc_read_pointer(Tuplestorestate *state, int eflags);
+
+extern void tuplestore_select_read_pointer(Tuplestorestate *state, int ptr);
+
+extern void tuplestore_copy_read_pointer(Tuplestorestate *state,
+										 int srcptr, int destptr);
+
 extern bool tuplestore_gettupleslot(Tuplestorestate *state, bool forward,
 						TupleTableSlot *slot);
 extern bool tuplestore_advance(Tuplestorestate *state, bool forward);
 
-extern void tuplestore_end(Tuplestorestate *state);
-
 extern bool tuplestore_ateof(Tuplestorestate *state);
 
 extern void tuplestore_rescan(Tuplestorestate *state);
-extern void tuplestore_markpos(Tuplestorestate *state);
-extern void tuplestore_restorepos(Tuplestorestate *state);
+
+extern void tuplestore_end(Tuplestorestate *state);
 
 #endif   /* TUPLESTORE_H */