Combine two flag tests in GetSnapshotData().

anarazel · anarazel · commit 5fde047f2b41 · 2018-11-09T20:43:56.000-08:00
Previously the code checked PROC_IN_LOGICAL_DECODING and PROC_IN_VACUUM separately. As the relevant variable is marked as volatile, the compiler cannot combine the two tests. As GetSnapshotData() is pretty hot in a number of workloads, it's worthwhile to fix that. It'd also be a good idea to get rid of the volatiles altogether. But for one that's a larger patch, and for another, the code after this change still seems at least as easy to read as before. Author: Andres Freund Discussion: https://postgr.es/m/20181005172955.wyjb4fzcdzqtaxjq@alap3.anarazel.de
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
@@ -1589,14 +1589,11 @@ GetSnapshotData(Snapshot snapshot)
 			TransactionId xid;
 
 			/*
-			 * Backend is doing logical decoding which manages xmin
-			 * separately, check below.
+			 * Skip over backends doing logical decoding which manages xmin
+			 * separately (check below) and ones running LAZY VACUUM.
 			 */
-			if (pgxact->vacuumFlags & PROC_IN_LOGICAL_DECODING)
-				continue;
-
-			/* Ignore procs running LAZY VACUUM */
-			if (pgxact->vacuumFlags & PROC_IN_VACUUM)
+			if (pgxact->vacuumFlags &
+				(PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM))
 				continue;
 
 			/* Update globalxmin to be the smallest valid xmin */
