From d2088ae949993ad8e3aabc3b6a9cd77aa5cac957 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 6 May 2011 12:57:28 -0400 Subject: [PATCH] Move RegisterPredicateLockingXid() call to a safer place. The SSI patch inserted a call of RegisterPredicateLockingXid into GetNewTransactionId, which was a bad idea on a couple of grounds. First, it's not necessary to hold XidGenLock while manipulating that shared memory, and doing so is bad because XidGenLock is a high-contention lock that should be held for as short a time as possible. (Not to mention that it adds an entirely unnecessary deadlock hazard, since we must take SerializableXactHashLock as well.) Second, the specific place where it was put was between extending CLOG and advancing nextXid, which could result in unpleasant behavior in case of a failure there. Pull the call out to AssignTransactionId, which is much safer and arguably better from a modularity standpoint too. There is more work to do to clean up the failure-before-advancing-nextXid issue, but that is a separate change that will need to be back-patched. So for the moment I just want to make GetNewTransactionId look the same as it did in prior versions. --- src/backend/access/transam/varsup.c | 5 ----- src/backend/access/transam/xact.c | 7 +++++++ 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c index 500335bd6f..555bb134f5 100644 --- a/src/backend/access/transam/varsup.c +++ b/src/backend/access/transam/varsup.c @@ -21,7 +21,6 @@ #include "miscadmin.h" #include "postmaster/autovacuum.h" #include "storage/pmsignal.h" -#include "storage/predicate.h" #include "storage/proc.h" #include "utils/builtins.h" #include "utils/syscache.h" @@ -162,10 +161,6 @@ GetNewTransactionId(bool isSubXact) ExtendCLOG(xid); ExtendSUBTRANS(xid); - /* If it's top level, the predicate locking system also needs to know. */ - if (!isSubXact) - RegisterPredicateLockingXid(xid); - /* * Now advance the nextXid counter. This must not happen until after we * have successfully completed ExtendCLOG() --- if that routine fails, we diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c index 8a4c4eccd7..2ca1c14549 100644 --- a/src/backend/access/transam/xact.c +++ b/src/backend/access/transam/xact.c @@ -454,6 +454,13 @@ AssignTransactionId(TransactionState s) if (isSubXact) SubTransSetParent(s->transactionId, s->parent->transactionId, false); + /* + * If it's a top-level transaction, the predicate locking system needs to + * be told about it too. + */ + if (!isSubXact) + RegisterPredicateLockingXid(s->transactionId); + /* * Acquire lock on the transaction XID. (We assume this cannot block.) We * have to ensure that the lock is assigned to the transaction's own