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Commitd2088ae

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Move RegisterPredicateLockingXid() call to a safer place.
The SSI patch inserted a call of RegisterPredicateLockingXid intoGetNewTransactionId, which was a bad idea on a couple of grounds. First,it's not necessary to hold XidGenLock while manipulating that sharedmemory, and doing so is bad because XidGenLock is a high-contention lockthat should be held for as short a time as possible. (Not to mention thatit adds an entirely unnecessary deadlock hazard, since we must takeSerializableXactHashLock as well.) Second, the specific place where it wasput was between extending CLOG and advancing nextXid, which could result inunpleasant behavior in case of a failure there. Pull the call out toAssignTransactionId, which is much safer and arguably better from amodularity standpoint too.There is more work to do to clean up the failure-before-advancing-nextXidissue, 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 asit did in prior versions.
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‎src/backend/access/transam/varsup.c

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@@ -21,7 +21,6 @@
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#include"miscadmin.h"
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#include"postmaster/autovacuum.h"
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#include"storage/pmsignal.h"
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#include"storage/predicate.h"
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#include"storage/proc.h"
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#include"utils/builtins.h"
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#include"utils/syscache.h"
@@ -162,10 +161,6 @@ GetNewTransactionId(bool isSubXact)
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ExtendCLOG(xid);
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ExtendSUBTRANS(xid);
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/* If it's top level, the predicate locking system also needs to know. */
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if (!isSubXact)
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RegisterPredicateLockingXid(xid);
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/*
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* Now advance the nextXid counter. This must not happen until after we
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* have successfully completed ExtendCLOG() --- if that routine fails, we

‎src/backend/access/transam/xact.c

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@@ -454,6 +454,13 @@ AssignTransactionId(TransactionState s)
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if (isSubXact)
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SubTransSetParent(s->transactionId,s->parent->transactionId, false);
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/*
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* If it's a top-level transaction, the predicate locking system needs to
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* be told about it too.
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*/
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if (!isSubXact)
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RegisterPredicateLockingXid(s->transactionId);
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/*
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* Acquire lock on the transaction XID. (We assume this cannot block.) We
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* have to ensure that the lock is assigned to the transaction's own

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