Re: Bug #866: Cursor scrolling broken in 7.3.1 (works in 7.2.1)

If you need it right away, here is the patch for the unique-index
problem. This will be in 7.3.2.

regards, tom lane

*** src/backend/access/index/genam.c.orig Wed Sep 4 17:30:07 2002
--- src/backend/access/index/genam.c Wed Jan 8 14:25:44 2003
***************
*** 107,112 ****
--- 107,115 ----
/* mark cached function lookup data invalid; it will be set later */
scan->fn_getnext.fn_oid = InvalidOid;

+ scan->unique_tuple_pos = 0;
+ scan->unique_tuple_mark = 0;
+
pgstat_initstats(&scan->xs_pgstat_info, indexRelation);

/*
*** src/backend/access/index/indexam.c.orig Wed Sep 4 17:30:08 2002
--- src/backend/access/index/indexam.c Wed Jan 8 14:34:21 2003
***************
*** 308,313 ****
--- 308,315 ----
scan->kill_prior_tuple = false; /* for safety */
scan->keys_are_unique = false; /* may be set by amrescan */
scan->got_tuple = false;
+ scan->unique_tuple_pos = 0;
+ scan->unique_tuple_mark = 0;

OidFunctionCall2(procedure,
PointerGetDatum(scan),
***************
*** 360,365 ****
--- 362,369 ----
SCAN_CHECKS;
GET_SCAN_PROCEDURE(markpos, ammarkpos);

+ scan->unique_tuple_mark = scan->unique_tuple_pos;
+
OidFunctionCall1(procedure, PointerGetDatum(scan));
}

***************
*** 376,382 ****
GET_SCAN_PROCEDURE(restrpos, amrestrpos);

scan->kill_prior_tuple = false; /* for safety */
! scan->got_tuple = false;

OidFunctionCall1(procedure, PointerGetDatum(scan));
}
--- 380,392 ----
GET_SCAN_PROCEDURE(restrpos, amrestrpos);

scan->kill_prior_tuple = false; /* for safety */
!
! /*
! * We do not reset got_tuple; so if the scan is actually being
! * short-circuited by index_getnext, the effective position restoration
! * is done by restoring unique_tuple_pos.
! */
! scan->unique_tuple_pos = scan->unique_tuple_mark;

OidFunctionCall1(procedure, PointerGetDatum(scan));
}
***************
*** 398,403 ****
--- 408,439 ----

SCAN_CHECKS;

+ /*
+ * Can skip entering the index AM if we already got a tuple and it
+ * must be unique. Instead, we need a "short circuit" path that
+ * just keeps track of logical scan position (before/on/after tuple).
+ *
+ * Note that we hold the pin on the single tuple's buffer throughout
+ * the scan once we are in this state.
+ */
+ if (scan->keys_are_unique && scan->got_tuple)
+ {
+ if (ScanDirectionIsForward(direction))
+ {
+ if (scan->unique_tuple_pos <= 0)
+ scan->unique_tuple_pos++;
+ }
+ else if (ScanDirectionIsBackward(direction))
+ {
+ if (scan->unique_tuple_pos >= 0)
+ scan->unique_tuple_pos--;
+ }
+ if (scan->unique_tuple_pos == 0)
+ return heapTuple;
+ else
+ return NULL;
+ }
+
/* Release any previously held pin */
if (BufferIsValid(scan->xs_cbuf))
{
***************
*** 408,420 ****
/* just make sure this is false... */
scan->kill_prior_tuple = false;

- /*
- * Can skip entering the index AM if we already got a tuple and it
- * must be unique.
- */
- if (scan->keys_are_unique && scan->got_tuple)
- return NULL;
-
for (;;)
{
bool found;
--- 444,449 ----
***************
*** 474,479 ****
--- 503,514 ----

/* Success exit */
scan->got_tuple = true;
+
+ /*
+ * If we just fetched a known-unique tuple, then subsequent calls will
+ * go through the short-circuit code above. unique_tuple_pos has been
+ * initialized to 0, which is the correct state ("on row").
+ */

pgstat_count_index_getnext(&scan->xs_pgstat_info);

*** src/include/access/relscan.h.orig Wed Sep 4 17:31:07 2002
--- src/include/access/relscan.h Wed Jan 8 14:11:13 2003
***************
*** 70,75 ****
--- 70,84 ----

FmgrInfo fn_getnext; /* cached lookup info for AM's getnext fn */

+ /*
+ * If keys_are_unique and got_tuple are both true, we stop calling the
+ * index AM; it is then necessary for index_getnext to keep track of
+ * the logical scan position for itself. It does that using
+ * unique_tuple_pos: -1 = before row, 0 = on row, +1 = after row.
+ */
+ int unique_tuple_pos; /* logical position */
+ int unique_tuple_mark; /* logical marked position */
+
PgStat_Info xs_pgstat_info; /* statistics collector hook */
} IndexScanDescData;