Remove empty function BufmgrCommit().

This function has been a no-op for over a decade.  Even if bufmgr
regains a need to be called during commit, it seems unlikely that
the most appropriate call points would be precisely here, so it's not
doing us much good as a placeholder either.  Now, removing it probably
doesn't save any noticeable number of cycles --- but the main call is
inside the commit critical section, and the less work done there the
better.

Matthias van de Meent

Discussion: https://postgr.es/m/CAEze2Wi1=tLKbxZnXzcD+8fYKyKqBtivVakLQC_mYBsP4Y8qVA@mail.gmail.com

src/backend/access/transam/xact.c

@@ -1373,12 +1373,6 @@ RecordTransactionCommit(void)
 		replorigin = (replorigin_session_origin != InvalidRepOriginId &&
 					  replorigin_session_origin != DoNotReplicateId);
 
-		/*
-		 * Begin commit critical section and insert the commit XLOG record.
-		 */
-		/* Tell bufmgr and smgr to prepare for commit */
-		BufmgrCommit();
-
 		/*
 		 * Mark ourselves as within our "commit critical section".  This
 		 * forces any concurrent checkpoint to wait until we've updated
@@ -1400,6 +1394,9 @@ RecordTransactionCommit(void)
 		START_CRIT_SECTION();
 		MyProc->delayChkptFlags |= DELAY_CHKPT_START;
 
+		/*
+		 * Insert the commit XLOG record.
+		 */
 		XactLogCommitRecord(GetCurrentTransactionStopTimestamp(),
 							nchildren, children, nrels, rels,
 							ndroppedstats, droppedstats,
@@ -2536,9 +2533,6 @@ PrepareTransaction(void)
 
 	prepared_at = GetCurrentTimestamp();
 
-	/* Tell bufmgr and smgr to prepare for commit */
-	BufmgrCommit();
-
 	/*
 	 * Reserve the GID for this transaction. This could fail if the requested
 	 * GID is invalid or already in use.