Improve BackendXidGetPid() to only access allProcs on matching XID

michaelpq · michaelpq · commit e722846daf4a · 2023-09-08T10:00:29.000+09:00
Compilers are able to optimize that, but it makes the code slightly more readable this way. Author: Zhao Junwang Reviewed-by: Ashutosh Bapat Discussion: https://postgr.es/m/CAEG8a3+i9gtqF65B+g_puVaCQuf0rZC-EMqMyEjGFJYOqUUWfA@mail.gmail.com
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
@@ -3174,11 +3174,11 @@ BackendXidGetPid(TransactionId xid)
 
 	for (index = 0; index < arrayP->numProcs; index++)
 	{
-		int			pgprocno = arrayP->pgprocnos[index];
-		PGPROC	   *proc = &allProcs[pgprocno];
-
 		if (other_xids[index] == xid)
 		{
+			int			pgprocno = arrayP->pgprocnos[index];
+			PGPROC	   *proc = &allProcs[pgprocno];
+
 			result = proc->pid;
 			break;
 		}

Original file line number	Diff line number	Diff line change
`@@ -3174,11 +3174,11 @@ BackendXidGetPid(TransactionId xid)`
`3174`	`3174`
`3175`	`3175`	`for (index = 0; index < arrayP->numProcs; index++)`
`3176`	`3176`	`{`
`3177`		`- int pgprocno = arrayP->pgprocnos[index];`
`3178`		`- PGPROC *proc = &allProcs[pgprocno];`
`3179`		`-`
`3180`	`3177`	`if (other_xids[index] == xid)`
`3181`	`3178`	`{`
	`3179`	`+ int pgprocno = arrayP->pgprocnos[index];`
	`3180`	`+ PGPROC *proc = &allProcs[pgprocno];`
	`3181`	`+`
`3182`	`3182`	`result = proc->pid;`
`3183`	`3183`	`break;`
`3184`	`3184`	`}`