From 8b02f81af635357a2ee70d561fc023aa3950e0cb Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Mon, 15 Nov 2021 13:59:44 +0000
Subject: [PATCH v1] pg_waldump:error out with options --follow and --stats

pg_waldump options, --follow or -f(to keep polling once per second
for new WAL to appear) and --stats or -z don't work well together
i.e. the command stucks [1]. This patch emits an error.
---
 doc/src/sgml/ref/pg_waldump.sgml | 12 ++++++++++--
 src/bin/pg_waldump/pg_waldump.c  | 12 ++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/pg_waldump.sgml b/doc/src/sgml/ref/pg_waldump.sgml
index 432254d2d5..b97534ced0 100644
--- a/doc/src/sgml/ref/pg_waldump.sgml
+++ b/doc/src/sgml/ref/pg_waldump.sgml
@@ -95,7 +95,8 @@ PostgreSQL documentation
       <listitem>
        <para>
         After reaching the end of valid WAL, keep polling once per second for
-        new WAL to appear.
+        new WAL to appear.  Note that <option>--stats</option> cannot be
+        specified with this option.
        </para>
       </listitem>
      </varlistentry>
@@ -200,7 +201,9 @@ PostgreSQL documentation
        <para>
         Display summary statistics (number and size of records and
         full-page images) instead of individual records. Optionally
-        generate statistics per-record instead of per-rmgr.
+        generate statistics per-record instead of per-rmgr. Note
+        that <option>--follow</option> cannot be specified with
+        this option.
        </para>
       </listitem>
      </varlistentry>
@@ -261,6 +264,11 @@ PostgreSQL documentation
     <literal>.partial</literal>. If those files need to be read, <literal>.partial</literal>
     suffix needs to be removed from the file name.
   </para>
+
+  <para>
+    Only the specified timeline is displayed (or the default, if none is
+    specified). Records in other timelines are ignored.
+  </para>
  </refsect1>
 
  <refsect1>
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 1e3894b9c4..58d6e4b2bd 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -952,6 +952,18 @@ main(int argc, char **argv)
 		goto bad_argument;
 	}
 
+	/*
+	 * Mutually exclusive arguments
+	 */
+	if (config.follow && config.stats)
+	{
+		pg_log_error("%s and %s are incompatible options",
+					 "--follow", "--stats");
+		fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+				progname);
+		exit(1);
+	}
+
 	if (waldir != NULL)
 	{
 		/* validate path points to directory */
-- 
2.25.1