Revert "Use group updates when setting transaction status in clog."

This reverts commit ccce90b3.  This
optimization is unsafe, at least, of rollbacks and rollbacks to
savepoints, but I'm concerned there may be other problematic cases as
well.  Therefore, I've decided to revert this pending further
investigation.

src/backend/access/transam/twophase.c

@@ -176,7 +176,7 @@ static TwoPhaseStateData *TwoPhaseState;
 /*
  * Global transaction entry currently locked by us, if any.
  */
-GlobalTransaction MyLockedGxact = NULL;
+static GlobalTransaction MyLockedGxact = NULL;
 
 static bool twophaseExitRegistered = false;
 

src/backend/storage/lmgr/proc.c

@@ -186,7 +186,6 @@ InitProcGlobal(void)
 	ProcGlobal->walwriterLatch = NULL;
 	ProcGlobal->checkpointerLatch = NULL;
 	pg_atomic_init_u32(&ProcGlobal->procArrayGroupFirst, INVALID_PGPROCNO);
-	pg_atomic_init_u32(&ProcGlobal->clogGroupFirst, INVALID_PGPROCNO);
 
 	/*
 	 * Create and initialize all the PGPROC structures we'll need.  There are
@@ -409,14 +408,6 @@ InitProcess(void)
 	/* Initialize wait event information. */
 	MyProc->wait_event_info = 0;
 
-	/* Initialize fields for group transaction status update. */
-	MyProc->clogGroupMember = false;
-	MyProc->clogGroupMemberXid = InvalidTransactionId;
-	MyProc->clogGroupMemberXidStatus = TRANSACTION_STATUS_IN_PROGRESS;
-	MyProc->clogGroupMemberPage = -1;
-	MyProc->clogGroupMemberLsn = InvalidXLogRecPtr;
-	pg_atomic_init_u32(&MyProc->clogGroupNext, INVALID_PGPROCNO);
-
 	/*
 	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
 	 * on it.  That allows us to repoint the process latch, which so far

src/include/access/twophase.h

@@ -24,8 +24,6 @@
  */
 typedef struct GlobalTransactionData *GlobalTransaction;
 
-extern GlobalTransaction MyLockedGxact;
-
 /* GUC variable */
 extern int	max_prepared_xacts;
 
@@ -38,17 +36,6 @@ extern void PostPrepare_Twophase(void);
 extern PGPROC *TwoPhaseGetDummyProc(TransactionId xid);
 extern BackendId TwoPhaseGetDummyBackendId(TransactionId xid);
 
-/*
- * IsGXactActive
- *		Return true if there is a Global transaction entry currently
- *		locked by us.
- */
-static inline bool
-IsGXactActive(void)
-{
-	return MyLockedGxact ? true : false;
-}
-
 extern GlobalTransaction MarkAsPreparing(TransactionId xid, const char *gid,
 				TimestampTz prepared_at,
 				Oid owner, Oid databaseid);

src/include/storage/proc.h

@@ -14,7 +14,6 @@
 #ifndef _PROC_H_
 #define _PROC_H_
 
-#include "access/clog.h"
 #include "access/xlogdefs.h"
 #include "lib/ilist.h"
 #include "storage/latch.h"
@@ -162,17 +161,6 @@ struct PGPROC
 
 	uint32		wait_event_info;	/* proc's wait information */
 
-	/* Support for group transaction status update. */
-	bool		clogGroupMember;	/* true, if member of clog group */
-	pg_atomic_uint32 clogGroupNext;		/* next clog group member */
-	TransactionId clogGroupMemberXid;	/* transaction id of clog group member */
-	XidStatus	clogGroupMemberXidStatus;		/* transaction status of clog
-												 * group member */
-	int			clogGroupMemberPage;	/* clog page corresponding to
-										 * transaction id of clog group member */
-	XLogRecPtr	clogGroupMemberLsn;		/* WAL location of commit record for
-										 * clog group member */
-
 	/* Per-backend LWLock.  Protects fields below (but not group fields). */
 	LWLock		backendLock;
 
@@ -244,8 +232,6 @@ typedef struct PROC_HDR
 	PGPROC	   *bgworkerFreeProcs;
 	/* First pgproc waiting for group XID clear */
 	pg_atomic_uint32 procArrayGroupFirst;
-	/* First pgproc waiting for group transaction status update */
-	pg_atomic_uint32 clogGroupFirst;
 	/* WALWriter process's latch */
 	Latch	   *walwriterLatch;
 	/* Checkpointer process's latch */