Fix failure to set ActiveSnapshot while rewinding a cursor.

ActiveSnapshot needs to be set when we call ExecutorRewind because some
plan node types may execute user-defined functions during their ReScan
calls (nodeLimit.c does so, at least).  The wisdom of that is somewhat
debatable, perhaps, but for now the simplest fix is to make sure the
required context is valid.  Failure to do this typically led to a
null-pointer-dereference core dump, though it's possible that in more
complex cases a function could be executed with the wrong snapshot
leading to very subtle misbehavior.

Per report from Leif Jensen.  It's been broken for a long time, so
back-patch to all active branches.

diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index d5e735ec253021168b6709046a384ede1c398f9e..cb10f0359358b8c8489fe5ebbdd866f472d461b2 100644 (file)
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -1661,6 +1661,9 @@ DoPortalRunFetch(Portal portal,
 static void
 DoPortalRewind(Portal portal)
 {
+       QueryDesc  *queryDesc;
+
+       /* Rewind holdStore, if we have one */
        if (portal->holdStore)
        {
                MemoryContext oldcontext;
@@ -1669,8 +1672,15 @@ DoPortalRewind(Portal portal)
                tuplestore_rescan(portal->holdStore);
                MemoryContextSwitchTo(oldcontext);
        }
-       if (PortalGetQueryDesc(portal))
-               ExecutorRewind(PortalGetQueryDesc(portal));
+
+       /* Rewind executor, if active */
+       queryDesc = PortalGetQueryDesc(portal);
+       if (queryDesc)
+       {
+               PushActiveSnapshot(queryDesc->snapshot);
+               ExecutorRewind(queryDesc);
+               PopActiveSnapshot();
+       }
 
        portal->atStart = true;
        portal->atEnd = false;

diff --git a/src/test/regress/expected/portals.out b/src/test/regress/expected/portals.out
index 01152a939d3ff7637c63e4bbb032cd3f029e94fe..1dc22957d29f00412828409bffa21cac4b6d0f3f 100644 (file)
--- a/src/test/regress/expected/portals.out
+++ b/src/test/regress/expected/portals.out
@@ -1257,3 +1257,27 @@ FETCH ALL FROM c1;
 
 COMMIT;
 DROP TABLE cursor;
+-- Check rewinding a cursor containing a stable function in LIMIT,
+-- per bug report in 8336843.9833.1399385291498.JavaMail.root@quick
+begin;
+create function nochange(int) returns int
+  as 'select $1 limit 1' language sql stable;
+declare c cursor for select * from int8_tbl limit nochange(3);
+fetch all from c;
+        q1        |        q2        
+------------------+------------------
+              123 |              456
+              123 | 4567890123456789
+ 4567890123456789 |              123
+(3 rows)
+
+move backward all in c;
+fetch all from c;
+        q1        |        q2        
+------------------+------------------
+              123 |              456
+              123 | 4567890123456789
+ 4567890123456789 |              123
+(3 rows)
+
+rollback;

diff --git a/src/test/regress/sql/portals.sql b/src/test/regress/sql/portals.sql
index 02286c4096eaa0ead285f14b44742098f28d33db..3777c2868704fc651afe2472087d754b05254f98 100644 (file)
--- a/src/test/regress/sql/portals.sql
+++ b/src/test/regress/sql/portals.sql
@@ -470,3 +470,14 @@ UPDATE cursor SET a = 2;
 FETCH ALL FROM c1;
 COMMIT;
 DROP TABLE cursor;
+
+-- Check rewinding a cursor containing a stable function in LIMIT,
+-- per bug report in 8336843.9833.1399385291498.JavaMail.root@quick
+begin;
+create function nochange(int) returns int
+  as 'select $1 limit 1' language sql stable;
+declare c cursor for select * from int8_tbl limit nochange(3);
+fetch all from c;
+move backward all in c;
+fetch all from c;
+rollback;