Fix bogus coding in ExecAppendAsyncEventWait().

No configured-by-FDW events would result in "return" directly out of a
PG_TRY block, making the exception stack dangling.  Repair.

Oversight in commit 501cfd07d; back-patch to v14, like that commit, but
as we do not have this issue in HEAD (cf. commit 50c67c201), no need to
apply this patch to it.

In passing, improve a comment about the handling of in-process requests
in a postgres_fdw.c function called from this function.

Alexander Pyhalov, with comment adjustment/improvement by me.

Discussion: https://postgr.es/m/425fa29a429b21b0332737c42a4fdc70%40postgrespro.ru

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index b08b314f9fdc7332a463233216775f7d0ee1c38b..e3b9b8d44d89b56cf893d47101ae54908efc36a5 100644 (file)
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -6968,14 +6968,16 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)
        {
                /*
                 * This is the case when the in-process request was made by another
-                * Append.  Note that it might be useless to process the request,
-                * because the query might not need tuples from that Append anymore.
-                * If there are any child subplans of the same parent that are ready
-                * for new requests, skip the given request.  Likewise, if there are
-                * any configured events other than the postmaster death event, skip
-                * it.  Otherwise, process the in-process request, then begin a fetch
-                * to configure the event below, because we might otherwise end up
-                * with no configured events other than the postmaster death event.
+                * Append.  Note that it might be useless to process the request made
+                * by that Append, because the query might not need tuples from that
+                * Append anymore; so we avoid processing it to begin a fetch for the
+                * given request if possible.  If there are any child subplans of the
+                * same parent that are ready for new requests, skip the given
+                * request.  Likewise, if there are any configured events other than
+                * the postmaster death event, skip it.  Otherwise, process the
+                * in-process request, then begin a fetch to configure the event
+                * below, because we might otherwise end up with no configured events
+                * other than the postmaster death event.
                 */
                if (!bms_is_empty(requestor->as_needrequest))
                        return;

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index 68f13f2a43f2d11ba582cee09e107dd2800b73e7..0509ee22fc48f5ed0db1f010a9b9ee57155cc2d0 100644 (file)
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1034,26 +1034,25 @@ ExecAppendAsyncEventWait(AppendState *node)
                }
 
                /*
-                * No need for further processing if there are no configured events
-                * other than the postmaster death event.
+                * If there are no configured events other than the postmaster death
+                * event, we don't need to wait or poll.
                 */
                if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
+                       noccurred = 0;
+               else
                {
-                       FreeWaitEventSet(node->as_eventset);
-                       node->as_eventset = NULL;
-                       return;
-               }
+                       /* Return at most EVENT_BUFFER_SIZE events in one call. */
+                       if (nevents > EVENT_BUFFER_SIZE)
+                               nevents = EVENT_BUFFER_SIZE;
 
-               /* Return at most EVENT_BUFFER_SIZE events in one call. */
-               if (nevents > EVENT_BUFFER_SIZE)
-                       nevents = EVENT_BUFFER_SIZE;
-
-               /*
-                * If the timeout is -1, wait until at least one event occurs.  If the
-                * timeout is 0, poll for events, but do not wait at all.
-                */
-               noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
-                                                                        nevents, WAIT_EVENT_APPEND_READY);
+                       /*
+                        * If the timeout is -1, wait until at least one event occurs.  If
+                        * the timeout is 0, poll for events, but do not wait at all.
+                        */
+                       noccurred = WaitEventSetWait(node->as_eventset, timeout,
+                                                                                occurred_event, nevents,
+                                                                                WAIT_EVENT_APPEND_READY);
+               }
        }
        PG_FINALLY();
        {