Use XID passed down by the remote datanode, if its available, when

GetCurrentTransactionIdIfAny() is called.

The regular GetCurrentTransactionId() does the same, without actually storing
the XID in the transaction state. We don't store the XID when the connection is
from a datanode, to ensure that a duplicate XID is not stored. There are other
technique employed to ensure multiple backends can participate in the same
global transaction.

This bug was causing wrong results when a query needs datanode-datanode
connections and updates are made previously in the same transaction, via a
different connection

Per report by Arun Shaji

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 6f84a48f0327de6f0e55ae8c6c6976062c43b1f9..a32ac5f8f1729f76a6a7beb5cacd8b4d5d85ee1f 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -548,6 +548,14 @@ GetCurrentTransactionId(void)
 TransactionId
 GetCurrentTransactionIdIfAny(void)
 {
+#ifdef XCP
+       /*
+        * Return XID if its available from the remote node, without assigning to
+        * the transaction state
+        */
+       if (IsConnFromDatanode())
+               return GetNextTransactionId();
+#endif
        return CurrentTransactionState->transactionId;
 }