From d16f8c8e416d288bd4734ed5f14076b62ec8d153 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 2 Mar 2021 13:53:46 -0500
Subject: [PATCH] Mark default_transaction_read_only as GUC_REPORT.

This allows clients to find out the setting at connection time without
having to expend a query round trip to do so; which is helpful when
trying to identify read/write servers.  (One must also look at
in_hot_standby, but that's already GUC_REPORT, cf bf8a662c9.)
Modifying libpq to make use of this will come soon, but I felt it
cleaner to push the server change separately.

Haribabu Kommi, Greg Nancarrow, Vignesh C; reviewed at various times
by Laurenz Albe, Takayuki Tsunakawa, Peter Smith.

Discussion: https://postgr.es/m/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
---
 doc/src/sgml/libpq.sgml      | 4 +++-
 doc/src/sgml/protocol.sgml   | 4 +++-
 src/backend/utils/misc/guc.c | 3 ++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index c635b6570c1..42b02b0a00c 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -2191,6 +2191,7 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>server_encoding</varname>,
        <varname>client_encoding</varname>,
        <varname>application_name</varname>,
+       <varname>default_transaction_read_only</varname>,
        <varname>in_hot_standby</varname>,
        <varname>is_superuser</varname>,
        <varname>session_authorization</varname>,
@@ -2206,7 +2207,8 @@ const char *PQparameterStatus(const PGconn *conn, const char *paramName);
        <varname>IntervalStyle</varname> was not reported by releases before 8.4;
        <varname>application_name</varname> was not reported by releases before
        9.0;
-       <varname>in_hot_standby</varname> was not reported by releases before
+       <varname>default_transaction_read_only</varname> and
+       <varname>in_hot_standby</varname> were not reported by releases before
        14.)
        Note that
        <varname>server_version</varname>,
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index a51f2c9920b..43092fe62a6 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1278,6 +1278,7 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>server_encoding</varname>,
     <varname>client_encoding</varname>,
     <varname>application_name</varname>,
+    <varname>default_transaction_read_only</varname>,
     <varname>in_hot_standby</varname>,
     <varname>is_superuser</varname>,
     <varname>session_authorization</varname>,
@@ -1293,7 +1294,8 @@ SELCT 1/0;<!-- this typo is intentional -->
     <varname>IntervalStyle</varname> was not reported by releases before 8.4;
     <varname>application_name</varname> was not reported by releases before
     9.0;
-    <varname>in_hot_standby</varname> was not reported by releases before
+    <varname>default_transaction_read_only</varname> and
+    <varname>in_hot_standby</varname> were not reported by releases before
     14.)
     Note that
     <varname>server_version</varname>,
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index d626731723b..7167cff7c33 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1619,7 +1619,8 @@ static struct config_bool ConfigureNamesBool[] =
 	{
 		{"default_transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
 			gettext_noop("Sets the default read-only status of new transactions."),
-			NULL
+			NULL,
+			GUC_REPORT
 		},
 		&DefaultXactReadOnly,
 		false,