Allow parallel workers to cope with a newly-created session user ID.

Parallel workers failed after a sequence like
	BEGIN;
	CREATE USER foo;
	SET SESSION AUTHORIZATION foo;
because check_session_authorization could not see the uncommitted
pg_authid row for "foo".  This is because we ran RestoreGUCState()
in a separate transaction using an ordinary just-created snapshot.
The same disease afflicts any other GUC that requires catalog lookups
and isn't forgiving about the lookups failing.

To fix, postpone RestoreGUCState() into the worker's main transaction
after we've set up a snapshot duplicating the leader's.  This affects
check_transaction_isolation and check_transaction_deferrable, which
think they should only run during transaction start.  Make them
act like check_transaction_read_only, which already knows it should
silently accept the value when InitializingParallelWorker.

Per bug #18545 from Andrey Rachitskiy.  Back-patch to all
supported branches, because this has been wrong for awhile.

Discussion: https://postgr.es/m/18545-feba138862f19aaa@postgresql.org

diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 8613fc6fb547c05d30d01a44282dba2b3f2178a3..b9cf197d353b9ffda2e52fefed255d145bd5901d 100644 (file)
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1410,10 +1410,6 @@ ParallelWorkerMain(Datum main_arg)
    libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false);
    StartTransactionCommand();
    RestoreLibraryState(libraryspace);
-
-   /* Restore GUC values from launching backend. */
-   gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
-   RestoreGUCState(gucspace);
    CommitTransactionCommand();
 
    /* Crank up a transaction state appropriate to a parallel worker. */
@@ -1455,6 +1451,14 @@ ParallelWorkerMain(Datum main_arg)
     */
    InvalidateSystemCaches();
 
+   /*
+    * Restore GUC values from launching backend.  We can't do this earlier,
+    * because GUC check hooks that do catalog lookups need to see the same
+    * database state as the leader.
+    */
+   gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
+   RestoreGUCState(gucspace);
+
    /*
     * Restore current role id.  Skip verifying whether session user is
     * allowed to become this role and blindly restore the leader's state for

diff --git a/src/backend/commands/variable.c b/src/backend/commands/variable.c
index f44d942aa4d45cd3eddfc2b54326911ae6bd8538..e3f9f110d8765d17a97ef08e9c6c823bf88252f2 100644 (file)
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -577,14 +577,16 @@ check_transaction_read_only(bool *newval, void **extra, GucSource source)
  * We allow idempotent changes at any time, but otherwise this can only be
  * changed in a toplevel transaction that has not yet taken a snapshot.
  *
- * As in check_transaction_read_only, allow it if not inside a transaction.
+ * As in check_transaction_read_only, allow it if not inside a transaction,
+ * or if restoring state in a parallel worker.
  */
 bool
 check_transaction_isolation(int *newval, void **extra, GucSource source)
 {
    int         newXactIsoLevel = *newval;
 
-   if (newXactIsoLevel != XactIsoLevel && IsTransactionState())
+   if (newXactIsoLevel != XactIsoLevel &&
+       IsTransactionState() && !InitializingParallelWorker)
    {
        if (FirstSnapshotSet)
        {
@@ -619,6 +621,10 @@ check_transaction_isolation(int *newval, void **extra, GucSource source)
 bool
 check_transaction_deferrable(bool *newval, void **extra, GucSource source)
 {
+   /* Just accept the value when restoring state in a parallel worker */
+   if (InitializingParallelWorker)
+       return true;
+
    if (IsSubTransaction())
    {
        GUC_check_errcode(ERRCODE_ACTIVE_SQL_TRANSACTION);

diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 5a603f86b7366dbacd18080f8df658f4fcb04a51..68a629619a6eb4bd4725a6bfb1c485863c93e1e1 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1329,3 +1329,21 @@ SELECT 1 FROM tenk1_vw_sec
 (9 rows)
 
 rollback;
+-- test that a newly-created session role propagates to workers.
+begin;
+create role regress_parallel_worker;
+set session authorization regress_parallel_worker;
+select current_setting('session_authorization');
+     current_setting     
+-------------------------
+ regress_parallel_worker
+(1 row)
+
+set debug_parallel_query = 1;
+select current_setting('session_authorization');
+     current_setting     
+-------------------------
+ regress_parallel_worker
+(1 row)
+
+rollback;

diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index c7df8f775cee90d6975a27239aa2847468cedb32..1a0e7f144d02e90e626296c27eda1e678a409b44 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -511,3 +511,12 @@ SELECT 1 FROM tenk1_vw_sec
   WHERE (SELECT sum(f1) FROM int4_tbl WHERE f1 < unique1) < 100;
 
 rollback;
+
+-- test that a newly-created session role propagates to workers.
+begin;
+create role regress_parallel_worker;
+set session authorization regress_parallel_worker;
+select current_setting('session_authorization');
+set debug_parallel_query = 1;
+select current_setting('session_authorization');
+rollback;