Introduce FrontendProtocollIsV3 shorthand for PG_PROTOCOL_MAJOR(FrontendProtocol)speedup/frontend_protocol

Using the long version in postgres.c SocketBackend introduces
noticeable pipeline stalls.

pgbench -v -h /tmp/ -U andres -T 200 -c3 -j3 -s 30 -S -M prepared pgbench
goes from 23221 to 25128

4 files changed, 22 insertions, 6 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index c0cf0336a1..9b97c268e8 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -1678,6 +1678,10 @@ retry1:
 	 * we fail during startup.
 	 */
 	FrontendProtocol = proto;
+	if(PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
+		FrontendProtocollIsV3 = true;
+	else
+		FrontendProtocollIsV3 = false;
 
 	/* Check we can handle the protocol the frontend is using. */
 
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index a07661f02a..794e44d0f6 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -362,7 +362,7 @@ SocketBackend(StringInfo inBuf)
 	{
 		case 'Q':				/* simple query */
 			doing_extended_query_message = false;
-			if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
+			if (!FrontendProtocollIsV3)
 			{
 				/* old style without length word; convert */
 				if (pq_getstring(inBuf))
@@ -393,7 +393,7 @@ SocketBackend(StringInfo inBuf)
 		case 'P':				/* parse */
 			doing_extended_query_message = true;
 			/* these are only legal in protocol 3 */
-			if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
+			if (!FrontendProtocollIsV3)
 				ereport(FATAL,
 						(errcode(ERRCODE_PROTOCOL_VIOLATION),
 						 errmsg("invalid frontend message type %d", qtype)));
@@ -405,7 +405,7 @@ SocketBackend(StringInfo inBuf)
 			/* mark not-extended, so that a new error doesn't begin skip */
 			doing_extended_query_message = false;
 			/* only legal in protocol 3 */
-			if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
+			if (!FrontendProtocollIsV3)
 				ereport(FATAL,
 						(errcode(ERRCODE_PROTOCOL_VIOLATION),
 						 errmsg("invalid frontend message type %d", qtype)));
@@ -416,7 +416,7 @@ SocketBackend(StringInfo inBuf)
 		case 'f':				/* copy fail */
 			doing_extended_query_message = false;
 			/* these are only legal in protocol 3 */
-			if (PG_PROTOCOL_MAJOR(FrontendProtocol) < 3)
+			if (!FrontendProtocollIsV3)
 				ereport(FATAL,
 						(errcode(ERRCODE_PROTOCOL_VIOLATION),
 						 errmsg("invalid frontend message type %d", qtype)));
@@ -440,7 +440,7 @@ SocketBackend(StringInfo inBuf)
 	 * after the type code; we can read the message contents independently of
 	 * the type.
 	 */
-	if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
+	if (FrontendProtocollIsV3)
 	{
 		if (pq_getmessage(inBuf, 0))
 			return EOF;			/* suitable message already logged */
@@ -3365,6 +3365,10 @@ process_postgres_switches(int argc, char *argv[], GucContext ctx)
 				 */
 				if (secure)
 					FrontendProtocol = (ProtocolVersion) atoi(optarg);
+				if(PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
+					FrontendProtocollIsV3 = true;
+				else
+					FrontendProtocollIsV3 = false;
 				break;
 
 			case 'W':
@@ -3689,7 +3693,7 @@ PostgresMain(int argc, char *argv[], const char *username)
 	 * Send this backend's cancellation info to the frontend.
 	 */
 	if (whereToSendOutput == DestRemote &&
-		PG_PROTOCOL_MAJOR(FrontendProtocol) >= 2)
+		FrontendProtocollIsV3)
 	{
 		StringInfoData buf;
 
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index c4c41544a2..b1b793e7db 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -25,6 +25,13 @@
 
 
 ProtocolVersion FrontendProtocol;
+/*
+ * Using PG_PROTOCOL_MAJOR(FrontendProtocol) < 3 all the time in
+ * postgres.c causes a noticeable amount of pipeline stalls. So we
+ * out-of-online that computation.
+ */
+bool FrontendProtocollIsV3;
+
 
 volatile bool InterruptPending = false;
 volatile bool QueryCancelPending = false;
diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
index 77e190fd1a..fd62b5bde0 100644
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -183,6 +183,7 @@ typedef struct Port
 
 
 extern ProtocolVersion FrontendProtocol;
+extern bool FrontendProtocollIsV3;
 
 /* TCP keepalives configuration. These are no-ops on an AF_UNIX socket. */