I wrote:
> [ dept of second thoughts... ] Actually, given that he said FOR UPDATE,
> the plan should be propagating the tuple identity through to top level
> so that execMain can do its thing. So in principle we could probably
> get the information without widespread changes. This would fit
> reasonably well with the spec's requirements too --- any but trivial
> cursors are not deemed updatable unless you say FOR UPDATE. But it
> would mean two completely independent implementations within
> execCurrent.c...
Here's a draft patch (no docs, no regression test) for that. It doesn't
look as ugly as I expected. Comments? I'm hesitant to call this a bug
fix, and we are past feature freeze ...
regards, tom lane
Index: src/backend/executor/execCurrent.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/execCurrent.c,v
retrieving revision 1.7
diff -c -r1.7 execCurrent.c
*** src/backend/executor/execCurrent.c 12 May 2008 00:00:48 -0000 1.7
--- src/backend/executor/execCurrent.c 15 Nov 2008 00:04:17 -0000
***************
*** 46,51 ****
--- 46,53 ----
char *table_name;
Portal portal;
QueryDesc *queryDesc;
+ ExecRowMark *erm;
+ ListCell *lc;
ScanState *scanstate;
bool lisnull;
Oid tuple_tableoid;
***************
*** 86,91 ****
--- 88,140 ----
cursor_name)));
/*
+ * If the query uses FOR UPDATE, look through the executor's state for
that
+ * to see if we can identify the target row that way. We succeed if
there
+ * is exactly one FOR UPDATE item for the requested table. (Note:
+ * presently, FOR UPDATE is not allowed on inheritance trees, so there
is
+ * no need to worry about whether a FOR UPDATE item is currently valid.)
+ */
+ erm = NULL;
+ foreach(lc, queryDesc->estate->es_rowMarks)
+ {
+ ExecRowMark *thiserm = (ExecRowMark *) lfirst(lc);
+
+ if (RelationGetRelid(thiserm->relation) == table_oid)
+ {
+ if (erm)
+ {
+ /* multiple references to desired relation */
+ erm = NULL;
+ break;
+ }
+ erm = thiserm;
+ }
+ }
+
+ if (erm)
+ {
+ /*
+ * Okay, we were able to identify the target FOR UPDATE item.
+ *
+ * The cursor must have a current result row: per the SQL spec,
it's
+ * an error if not.
+ */
+ if (portal->atStart || portal->atEnd)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_CURSOR_STATE),
+ errmsg("cursor \"%s\" is not
positioned on a row",
+ cursor_name)));
+ /* Return the currently scanned TID */
+ if (ItemPointerIsValid(&(erm->curCtid)))
+ {
+ *current_tid = erm->curCtid;
+ return true;
+ }
+ /* Inactive scan? Probably can't happen at the moment */
+ return false;
+ }
+
+ /*
* Dig through the cursor's plan to find the scan node. Fail if it's
not
* there or buried underneath aggregation.
*/
Index: src/backend/executor/execMain.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/execMain.c,v
retrieving revision 1.315
diff -c -r1.315 execMain.c
*** src/backend/executor/execMain.c 6 Nov 2008 20:51:14 -0000 1.315
--- src/backend/executor/execMain.c 15 Nov 2008 00:04:17 -0000
***************
*** 602,607 ****
--- 602,608 ----
erm->noWait = rc->noWait;
/* We'll set up ctidAttno below */
erm->ctidAttNo = InvalidAttrNumber;
+ ItemPointerSetInvalid(&(erm->curCtid));
estate->es_rowMarks = lappend(estate->es_rowMarks, erm);
}
***************
*** 1442,1447 ****
--- 1443,1451 ----
elog(ERROR,
"unrecognized heap_lock_tuple status: %u",
test);
}
+
+ /* Remember tuple TID for WHERE CURRENT
OF */
+ erm->curCtid = tuple.t_self;
}
}
Index: src/include/nodes/execnodes.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/nodes/execnodes.h,v
retrieving revision 1.194
diff -c -r1.194 execnodes.h
*** src/include/nodes/execnodes.h 31 Oct 2008 19:37:56 -0000 1.194
--- src/include/nodes/execnodes.h 15 Nov 2008 00:04:17 -0000
***************
*** 376,381 ****
--- 376,382 ----
bool forUpdate; /* true = FOR UPDATE, false =
FOR SHARE */
bool noWait; /* NOWAIT option */
AttrNumber ctidAttNo; /* resno of its ctid junk
attribute */
+ ItemPointerData curCtid; /* ctid of currently locked tuple */
} ExecRowMark;
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