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 95ab3722d303fc5b2019fe6eeb014404c616a0c9..ad290b8506d37d5961e82fe4e4a7054c0c3d0224 100644 (file)
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1401,10 +1401,6 @@ 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. */
@@ -1446,6 +1442,14 @@ 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 7fd3ca3a42318fd1385034868530778826c0baab..974280dd56834903983dded88bad87ae84256ef6 100644 (file)
--- a/src/backend/commands/variable.c
+++ b/src/backend/commands/variable.c
@@ -519,14 +519,16 @@ 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_XactIsoLevel(int *newval, void **extra, GucSource source)
 {
    int         newXactIsoLevel = *newval;
 
-   if (newXactIsoLevel != XactIsoLevel && IsTransactionState())
+   if (newXactIsoLevel != XactIsoLevel &&
+       IsTransactionState() && !InitializingParallelWorker)
    {
        if (FirstSnapshotSet)
        {
@@ -561,6 +563,10 @@ check_XactIsoLevel(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 cdbaa4a7b6144a60141f150f399bdddcb125e2f3..d22898580387fb3c99c7643f855aad16ff30d60b 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1221,3 +1221,21 @@ 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 force_parallel_mode = 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 43adb05b7a30170673323557ca8de62d7c313467..86eb50c8c379242275a96b6191d191c27dc34d87 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -464,3 +464,12 @@ 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 force_parallel_mode = 1;
+select current_setting('session_authorization');
+rollback;