Re: SSI patch renumbered existing 2PC resource managers?? - Mailing list pgsql-hackers

Bruce Momjian wrote:
> > This argument seems a tad peculiar, since the *entire* *point* of
> > pg_upgrade is to push physical files from one installation into another
> > even though compatibility isn't guaranteed.  It is the program's duty to
> > understand enough to know whether it can transport the cluster's state
> > safely.  Not to arbitrarily discard state because it might possibly not
> > be transportable.
>
> Well, pg_upgrade succeeds because it does as little as necessary to do
> the migration, relying on pg_dump to do much of the migration work at
> the catalog level.  pg_upgrade tries to be involved as little as
> possible with the Postgres code so it doesn't have to be changed
> regularly between major versions.
>
> The prepared transaction case seems ugly enough that we don't want
> pg_upgrade to have to check every major release if anything changed
> about the data stored in prepared transactions.  This is the same reason
> pg_upgrade doesn't transfer WAL files from the old cluster, just pg_clog
> files (which rarely changes its format).

I have applied the attached pg_upgrade patch to head and 9.1 to fail if
prepared transactions are in the old or new cluster.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +
diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
new file mode 100644
index fdec6e3..376d25a
*** a/contrib/pg_upgrade/check.c
--- b/contrib/pg_upgrade/check.c
*************** static void check_old_cluster_has_new_cl
*** 16,21 ****
--- 16,22 ----
  static void check_locale_and_encoding(ControlData *oldctrl,
                            ControlData *newctrl);
  static void check_is_super_user(ClusterInfo *cluster);
+ static void check_for_prepared_transactions(ClusterInfo *cluster);
  static void check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster);
  static void check_for_reg_data_type_usage(ClusterInfo *cluster);

*************** check_old_cluster(bool live_check,
*** 65,70 ****
--- 66,72 ----
       * Check for various failure cases
       */
      check_is_super_user(&old_cluster);
+     check_for_prepared_transactions(&old_cluster);
      check_for_reg_data_type_usage(&old_cluster);
      check_for_isn_and_int8_passing_mismatch(&old_cluster);

*************** check_new_cluster(void)
*** 117,122 ****
--- 119,125 ----
      get_db_and_rel_infos(&new_cluster);

      check_new_cluster_is_empty();
+     check_for_prepared_transactions(&new_cluster);
      check_old_cluster_has_new_cluster_dbs();

      check_loadable_libraries();
*************** check_is_super_user(ClusterInfo *cluster
*** 507,512 ****
--- 510,545 ----


  /*
+  *    check_for_prepared_transactions()
+  *
+  *    Make sure there are no prepared transactions because the storage format
+  *    might have changed.
+  */
+ static void
+ check_for_prepared_transactions(ClusterInfo *cluster)
+ {
+     PGresult   *res;
+     PGconn       *conn = connectToServer(cluster, "template1");
+
+     prep_status("Checking for prepared transactions");
+
+     res = executeQueryOrDie(conn,
+                             "SELECT * "
+                             "FROM pg_catalog.pg_prepared_xact()");
+
+     if (PQntuples(res) != 0)
+         pg_log(PG_FATAL, "The %s cluster contains prepared transactions\n",
+                CLUSTER_NAME(cluster));
+
+     PQclear(res);
+
+     PQfinish(conn);
+
+     check_ok();
+ }
+
+
+ /*
   *    check_for_isn_and_int8_passing_mismatch()
   *
   *    contrib/isn relies on data type int8, and in 8.4 int8 can now be passed