v5-0002-Remove-PGPROC-s-redundant-pgprocno-member.patch

From 562657ea3f7be124a6c6b6d1e7450da2431a54a0 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Thu, 11 Mar 2021 23:09:11 +1300
Subject: [PATCH v5 2/2] Remove PGPROC's redundant pgprocno member.

It's derivable with pointer arithmetic.

Author: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGLYRyDaneEwz5Uya_OgFLMx5BgJfkQSD%3Dq9HmwsfRRb-w%40mail.gmail.com
---
 src/backend/access/transam/clog.c             |  2 +-
 src/backend/access/transam/twophase.c         |  3 +--
 src/backend/access/transam/xlog.c             |  2 +-
 src/backend/postmaster/bgwriter.c             |  2 +-
 src/backend/postmaster/pgarch.c               |  2 +-
 src/backend/storage/buffer/bufmgr.c           |  6 +++---
 src/backend/storage/ipc/procarray.c           |  6 +++---
 src/backend/storage/lmgr/condition_variable.c | 12 ++++++------
 src/backend/storage/lmgr/lwlock.c             |  6 +++---
 src/backend/storage/lmgr/predicate.c          |  2 +-
 src/backend/storage/lmgr/proc.c               |  8 +++-----
 src/backend/utils/adt/lockfuncs.c             |  1 +
 src/include/storage/lock.h                    |  2 +-
 src/include/storage/proc.h                    |  6 +++++-
 14 files changed, 31 insertions(+), 29 deletions(-)

diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 3ea16a270a..d0557f6c55 100644
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -464,7 +464,7 @@ TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status,
 
 		if (pg_atomic_compare_exchange_u32(&procglobal->clogGroupFirst,
 										   &nextidx,
-										   (uint32) proc->pgprocno))
+										   (uint32) GetPGProcNumber(proc)))
 			break;
 	}
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 6d3efb49a4..0fe8a59cf0 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -279,7 +279,7 @@ TwoPhaseShmemInit(void)
 			TwoPhaseState->freeGXacts = &gxacts[i];
 
 			/* associate it with a PGPROC assigned by InitProcGlobal */
-			gxacts[i].pgprocno = PreparedXactProcs[i].pgprocno;
+			gxacts[i].pgprocno = GetPGProcNumber(&PreparedXactProcs[i]);
 
 			/*
 			 * Assign a unique ID for each dummy proc, so that the range of
@@ -456,7 +456,6 @@ MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid, const char *gid,
 
 	/* Initialize the PGPROC entry */
 	MemSet(proc, 0, sizeof(PGPROC));
-	proc->pgprocno = gxact->pgprocno;
 	SHMQueueElemInit(&(proc->links));
 	proc->waitStatus = PROC_WAIT_STATUS_OK;
 	/* We set up the gxact's VXID as InvalidBackendId/XID */
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1574362724..576ba061d8 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1666,7 +1666,7 @@ WALInsertLockAcquire(void)
 	static int	lockToTry = -1;
 
 	if (lockToTry == -1)
-		lockToTry = MyProc->pgprocno % NUM_XLOGINSERT_LOCKS;
+		lockToTry = GetPGProcNumber(MyProc) % NUM_XLOGINSERT_LOCKS;
 	MyLockNo = lockToTry;
 
 	/*
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 5584f4bc24..8c812e906d 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -333,7 +333,7 @@ BackgroundWriterMain(void)
 		if (rc == WL_TIMEOUT && can_hibernate && prev_hibernate)
 		{
 			/* Ask for notification at next buffer allocation */
-			StrategyNotifyBgWriter(MyProc->pgprocno);
+			StrategyNotifyBgWriter(GetPGProcNumber(MyProc));
 			/* Sleep ... */
 			(void) WaitLatch(MyLatch,
 							 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 74a7d7c4d0..68de7ee3b8 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -196,7 +196,7 @@ PgArchiverMain(void)
 	 * Advertise our pgprocno so that backends can use our latch to wake us up
 	 * while we're sleeping.
 	 */
-	PgArch->pgprocno = MyProc->pgprocno;
+	PgArch->pgprocno = GetPGProcNumber(MyProc);
 
 	pgarch_MainLoop();
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index fb86c8706c..ad95e2f938 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3995,7 +3995,7 @@ UnlockBuffers(void)
 		 * got a cancel/die interrupt before getting the signal.
 		 */
 		if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
-			buf->wait_backend_pgprocno == MyProc->pgprocno)
+			buf->wait_backend_pgprocno == GetPGProcNumber(MyProc))
 			buf_state &= ~BM_PIN_COUNT_WAITER;
 
 		UnlockBufHdr(buf, buf_state);
@@ -4131,7 +4131,7 @@ LockBufferForCleanup(Buffer buffer)
 			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 			elog(ERROR, "multiple backends attempting to wait for pincount 1");
 		}
-		bufHdr->wait_backend_pgprocno = MyProc->pgprocno;
+		bufHdr->wait_backend_pgprocno = GetPGProcNumber(MyProc);
 		PinCountWaitBuf = bufHdr;
 		buf_state |= BM_PIN_COUNT_WAITER;
 		UnlockBufHdr(bufHdr, buf_state);
@@ -4202,7 +4202,7 @@ LockBufferForCleanup(Buffer buffer)
 		 */
 		buf_state = LockBufHdr(bufHdr);
 		if ((buf_state & BM_PIN_COUNT_WAITER) != 0 &&
-			bufHdr->wait_backend_pgprocno == MyProc->pgprocno)
+			bufHdr->wait_backend_pgprocno == GetPGProcNumber(MyProc))
 			buf_state &= ~BM_PIN_COUNT_WAITER;
 		UnlockBufHdr(bufHdr, buf_state);
 
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index c7816fcfb3..a2f53a9ce9 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -492,7 +492,7 @@ ProcArrayAdd(PGPROC *proc)
 		Assert(allProcs[procno].pgxactoff == index);
 
 		/* If we have found our right position in the array, break */
-		if (arrayP->pgprocnos[index] > proc->pgprocno)
+		if (arrayP->pgprocnos[index] > GetPGProcNumber(proc))
 			break;
 	}
 
@@ -510,7 +510,7 @@ ProcArrayAdd(PGPROC *proc)
 			&ProcGlobal->statusFlags[index],
 			movecount * sizeof(*ProcGlobal->statusFlags));
 
-	arrayP->pgprocnos[index] = proc->pgprocno;
+	arrayP->pgprocnos[index] = GetPGProcNumber(proc);
 	proc->pgxactoff = index;
 	ProcGlobal->xids[index] = proc->xid;
 	ProcGlobal->subxidStates[index] = proc->subxidStatus;
@@ -789,7 +789,7 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
 
 		if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
 										   &nextidx,
-										   (uint32) proc->pgprocno))
+										   (uint32) GetPGProcNumber(proc)))
 			break;
 	}
 
diff --git a/src/backend/storage/lmgr/condition_variable.c b/src/backend/storage/lmgr/condition_variable.c
index 80d70c154c..d0728d17bd 100644
--- a/src/backend/storage/lmgr/condition_variable.c
+++ b/src/backend/storage/lmgr/condition_variable.c
@@ -57,7 +57,7 @@ ConditionVariableInit(ConditionVariable *cv)
 void
 ConditionVariablePrepareToSleep(ConditionVariable *cv)
 {
-	int			pgprocno = MyProc->pgprocno;
+	int			pgprocno = GetPGProcNumber(MyProc);
 
 	/*
 	 * If some other sleep is already prepared, cancel it; this is necessary
@@ -181,10 +181,10 @@ ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
 		 * guarantee not to return spuriously, we'll avoid this obvious case.
 		 */
 		SpinLockAcquire(&cv->mutex);
-		if (!proclist_contains(&cv->wakeup, MyProc->pgprocno, cvWaitLink))
+		if (!proclist_contains(&cv->wakeup, GetPGProcNumber(MyProc), cvWaitLink))
 		{
 			done = true;
-			proclist_push_tail(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
+			proclist_push_tail(&cv->wakeup, GetPGProcNumber(MyProc), cvWaitLink);
 		}
 		SpinLockRelease(&cv->mutex);
 
@@ -234,8 +234,8 @@ ConditionVariableCancelSleep(void)
 		return;
 
 	SpinLockAcquire(&cv->mutex);
-	if (proclist_contains(&cv->wakeup, MyProc->pgprocno, cvWaitLink))
-		proclist_delete(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
+	if (proclist_contains(&cv->wakeup, GetPGProcNumber(MyProc), cvWaitLink))
+		proclist_delete(&cv->wakeup, GetPGProcNumber(MyProc), cvWaitLink);
 	else
 		signaled = true;
 	SpinLockRelease(&cv->mutex);
@@ -285,7 +285,7 @@ ConditionVariableSignal(ConditionVariable *cv)
 void
 ConditionVariableBroadcast(ConditionVariable *cv)
 {
-	int			pgprocno = MyProc->pgprocno;
+	int			pgprocno = GetPGProcNumber(MyProc);
 	PGPROC	   *proc = NULL;
 	bool		have_sentinel = false;
 
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 862097352b..e3cef6700a 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -1080,9 +1080,9 @@ LWLockQueueSelf(LWLock *lock, LWLockMode mode)
 
 	/* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
 	if (mode == LW_WAIT_UNTIL_FREE)
-		proclist_push_head(&lock->waiters, MyProc->pgprocno, lwWaitLink);
+		proclist_push_head(&lock->waiters, GetPGProcNumber(MyProc), lwWaitLink);
 	else
-		proclist_push_tail(&lock->waiters, MyProc->pgprocno, lwWaitLink);
+		proclist_push_tail(&lock->waiters, GetPGProcNumber(MyProc), lwWaitLink);
 
 	/* Can release the mutex now */
 	LWLockWaitListUnlock(lock);
@@ -1122,7 +1122,7 @@ LWLockDequeueSelf(LWLock *lock)
 	 */
 	proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
 	{
-		if (iter.cur == MyProc->pgprocno)
+		if (iter.cur == GetPGProcNumber(MyProc))
 		{
 			found = true;
 			proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index fbc0caca5c..508c8bb37f 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -3674,7 +3674,7 @@ ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe)
 				PGPROC	   *proc;
 
 				proc = BackendIdGetProc(roXact->vxid.backendId);
-				ProcSendSignal(proc->pgprocno);
+				ProcSendSignal(GetPGProcNumber(proc));
 			}
 
 			possibleUnsafeConflict = nextConflict;
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 7f2111c6e0..1321786857 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -227,7 +227,6 @@ InitProcGlobal(void)
 			InitSharedLatch(&(procs[i].procLatch));
 			LWLockInitialize(&(procs[i].fpInfoLock), LWTRANCHE_LOCK_FASTPATH);
 		}
-		procs[i].pgprocno = i;
 
 		/*
 		 * Newly created PGPROCs for normal backends, autovacuum and bgworkers
@@ -1947,10 +1946,9 @@ BecomeLockGroupMember(PGPROC *leader, int pid)
 
 	/*
 	 * Get lock protecting the group fields.  Note LockHashPartitionLockByProc
-	 * accesses leader->pgprocno in a PGPROC that might be free.  This is safe
-	 * because all PGPROCs' pgprocno fields are set during shared memory
-	 * initialization and never change thereafter; so we will acquire the
-	 * correct lock even if the leader PGPROC is in process of being recycled.
+	 * takes a PGPROC that might be free, but it uses only its address.  We
+	 * will acquire the correct lock even if the leader PGPROC is in the
+	 * process of being recycled.
 	 */
 	leader_lwlock = LockHashPartitionLockByProc(leader);
 	LWLockAcquire(leader_lwlock, LW_EXCLUSIVE);
diff --git a/src/backend/utils/adt/lockfuncs.c b/src/backend/utils/adt/lockfuncs.c
index 5dc0a5882c..020f76e431 100644
--- a/src/backend/utils/adt/lockfuncs.c
+++ b/src/backend/utils/adt/lockfuncs.c
@@ -18,6 +18,7 @@
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "storage/predicate_internals.h"
+#include "storage/proc.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
 
diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index 9b2a421c32..c8e1b0ce1a 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -531,7 +531,7 @@ typedef enum
  * used for a given lock group is determined by the group leader's pgprocno.
  */
 #define LockHashPartitionLockByProc(leader_pgproc) \
-	LockHashPartitionLock((leader_pgproc)->pgprocno)
+	LockHashPartitionLock(GetPGProcNumber(leader_pgproc))
 
 /*
  * function prototypes
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 7c1e2efe30..435876772b 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -147,7 +147,6 @@ struct PGPROC
 
 	int			pgxactoff;		/* offset into various ProcGlobal->arrays with
 								 * data mirrored from this PGPROC */
-	int			pgprocno;
 
 	/* These fields are zero while a backend is still starting up: */
 	BackendId	backendId;		/* This backend's backend ID (if assigned) */
@@ -311,6 +310,9 @@ extern PGDLLIMPORT PGPROC *MyProc;
  * When entering a PGPROC for 2PC transactions with ProcArrayAdd(), the data
  * in the dense arrays is initialized from the PGPROC while it already holds
  * ProcArrayLock.
+ *
+ * Shared memory data structures can refer to PGPROCs by index in allProcs.
+ * See GetPGProcNumber() and GetPGProcByNumber().
  */
 typedef struct PROC_HDR
 {
@@ -362,6 +364,8 @@ extern PGPROC *PreparedXactProcs;
 
 /* Accessor for PGPROC given a pgprocno. */
 #define GetPGProcByNumber(n) (&ProcGlobal->allProcs[(n)])
+/* Accessor for pgprocno given a pointer to PGPROC. */
+#define GetPGProcNumber(proc) ((proc) - ProcGlobal->allProcs)
 
 /*
  * We set aside some extra PGPROC structures for auxiliary processes,
-- 
2.30.2