Added support for two new pieces of functionality.

1) Support for DDL and utility command synchronisation among Coordinators.

DDL is now synchronized amongst multiple coordinators. Previously, after
DDL it was required to use an extra utility to resync the nodes and
restart other Coordinators. This is no longer necessary.

DDL support works also with common BEGIN, COMMIT and ROLLBACK instructions
in the cluster.

DDL may be initiated at any node. Each Coordinator can connect to any
other one.

Just as Coordinators use pools for connecting to Data Nodes, Coordinators
now use pools for connecting to the other Coordinators.

2) Support for PREPARE TRANSACTION and COMMIT TRANSACTION, ROLLBACK PREPARED.

When a transaction is prepared or committed, based on the SQL, it will only
execute on the involved nodes, including DDL on Coordinators.

GTM is used track which xid and nodes are involved in the transaction,
identified by the user or application specified transaction identifier,
when it is prepared.

New GUCs
--------
There are some new GUCs for handling Coordinator communication

num_coordinators
coordinator_hosts
coordinator_ports
coordinator_users
coordinator_passwords

In addition, a new GUC replaces coordinator_id:

pgxc_node_id

Open Issues
-----------
Implicit two phase commit (client in autocommit mode, but distributed
transaction required because of multiple nodes) does not first prepare
on the originating coordinator before committing, if DDL is involved.
We really should prepare here before committing on all nodes.

We also need to add a bit of special handling for COMMIT PREPARED.
If there is an error, and it got committed on some nodes, we still
should force it to be committed on the originating coordinator, if
involved, and still return an error of some sort that it was partially
committed. (When the downed node recovers, in the future it will determine
if any other node has committed the transaction, and if so, it, too, must
commit.) It is a pretty rare case, but we should handle it.

With this current configuration, DDL will fail if at least one
Coordinator is down.  In the future, we will make this more flexible.

Written by Michael Paquier

2 files changed, 2 insertions, 5 deletions

diff --git a/src/include/utils/guc_tables.h b/src/include/utils/guc_tables.h
index 9c87386288..b69dd3d6b3 100644
--- a/src/include/utils/guc_tables.h
+++ b/src/include/utils/guc_tables.h
@@ -78,7 +78,8 @@ enum config_group
 	CUSTOM_OPTIONS,
 	DEVELOPER_OPTIONS,
 	DATA_NODES,
-	GTM
+	GTM,
+	COORDINATORS
 };
 
 /*
diff --git a/src/include/utils/timestamp.h b/src/include/utils/timestamp.h
index 7c8e744915..31d110ad27 100644
--- a/src/include/utils/timestamp.h
+++ b/src/include/utils/timestamp.h
@@ -23,10 +23,6 @@
 #include "utils/int8.h"
 #endif
 
-#ifdef PGXC
-#include "pgxc/pgxc.h"
-#endif
-
 /*
  * Timestamp represents absolute time.
  *