From afca5e895e07279049f272396e40bdb78ae61d0e Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 21 Oct 2021 13:21:43 +0900
Subject: [PATCH v9 1/2] doc: Describe calculation method of streaming start
 for pg_receivewal

The documentation was unprecise about the fact that the current WAL
flush location is used if nothing can be found on the local archive
directory describe, independently of the compression used by each
segment (ZLIB or uncompressed).
---
 doc/src/sgml/ref/pg_receivewal.sgml | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/doc/src/sgml/ref/pg_receivewal.sgml b/doc/src/sgml/ref/pg_receivewal.sgml
index 45b544cf49..9adbddb657 100644
--- a/doc/src/sgml/ref/pg_receivewal.sgml
+++ b/doc/src/sgml/ref/pg_receivewal.sgml
@@ -75,6 +75,29 @@ PostgreSQL documentation
    one session available for the stream.
   </para>
 
+  <para>
+   The starting point of the write-ahead log streaming is calculated when
+   <application>pg_receivewal</application> starts:
+   <orderedlist>
+    <listitem>
+     <para>
+      First, scan the directory where the WAL segment files are written and
+      find the newest completed segment, using as starting point the beginning
+      of the next WAL segment file. This is calculated independently of the
+      compression method used to compress each segment.
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
+      If a starting point cannot be calculated with the previous method,
+      the latest WAL flush location is used as reported by the server from
+      a <literal>IDENTIFY_SYSTEM</literal> command.
+     </para>
+    </listitem>
+   </orderedlist>
+  </para>
+
   <para>
    If the connection is lost, or if it cannot be initially established,
    with a non-fatal error, <application>pg_receivewal</application> will
-- 
2.33.0