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 2b8bc2f58dd8e152f6085c92e51e415aa9cf800d..8606c009dd9d397dbaf9becc14544dc5370f7808 100644 (file)
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1414,10 +1414,6 @@ 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. */
@@ -1459,6 +1455,14 @@ 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 f0f2e076552410aa8170e64cc979b10b61b66ec3..f25563fa5f070a47657fc245180749adf9073377 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 d88353d496c824af5ac02af8cf7f0dc0787f7707..768b42c9293f9948f7eaeef38cbc31c7df50c57f 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1219,3 +1219,21 @@ 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 80c914dc02b0bc74e330beb89c1fad72364139c4..e98c759bb2512cff5c1bd90c281dae974f02ce7b 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -462,3 +462,12 @@ 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;