Fix order of arguments to SubTransSetParent().

ProcessTwoPhaseBuffer (formerly StandbyRecoverPreparedTransactions)
mixed up the parent and child XIDs when calling SubTransSetParent to
record the transactions' relationship in pg_subtrans.

Remarkably, analysis by Simon Riggs suggests that this doesn't lead to
visible problems (at least, not in non-Assert builds).  That might
explain why we'd not noticed it before.  Nonetheless, it's surely wrong.

This code was born broken, so back-patch to all supported branches.

Discussion: https://postgr.es/m/20110.1492905318@sss.pgh.pa.us

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0dd5b59ff46a40728ffb9caf98cc455508a02094..f3d239de6e12b6da2b7952ab475455283678acc1 100644 (file)
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1922,7 +1922,7 @@ StandbyRecoverPreparedTransactions(bool overwriteOK)
                                TransactionId subxid = subxids[i];
 
                                Assert(TransactionIdFollows(subxid, xid));
-                               SubTransSetParent(xid, subxid, overwriteOK);
+                               SubTransSetParent(subxid, xid, overwriteOK);
                        }
                }
        }