From bc62da6173e029e1fd25d13bbbe648f008be6b68 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Tue, 19 Sep 2023 16:11:38 +0200
Subject: [PATCH v2 6/7] doc: pg_resetwal: Add comments how the multipliers are
 derived

---
 doc/src/sgml/ref/pg_resetwal.sgml | 8 +++++++-
 src/bin/pg_resetwal/pg_resetwal.c | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/pg_resetwal.sgml b/doc/src/sgml/ref/pg_resetwal.sgml
index 1f9c4b69dd..8380f97c04 100644
--- a/doc/src/sgml/ref/pg_resetwal.sgml
+++ b/doc/src/sgml/ref/pg_resetwal.sgml
@@ -166,7 +166,8 @@ <title>Options</title>
    <command>pg_resetwal</command> is unable to determine appropriate values
    by reading <filename>pg_control</filename>.  Safe values can be determined as
    described below.  For values that take numeric arguments, hexadecimal
-   values can be specified by using the prefix <literal>0x</literal>.
+   values can be specified by using the prefix <literal>0x</literal>.  Note
+   that these instructions only apply with the standard block size of 8 kB.
   </para>
 
   <variablelist>
@@ -189,6 +190,7 @@ <title>Options</title>
       greatest file name in the same directory.  The file names are in
       hexadecimal.
      </para>
+      <!-- FIXME: multiplier? -->
     </listitem>
    </varlistentry>
 
@@ -272,6 +274,7 @@ <title>Options</title>
       names are in hexadecimal, so the easiest way to do this is to specify
       the option value in hexadecimal and append four zeroes.
      </para>
+     <!-- 65536 = SLRU_PAGES_PER_SEGMENT * BLCKSZ / sizeof(MultiXactOffset) -->
     </listitem>
    </varlistentry>
 
@@ -306,6 +309,7 @@ <title>Options</title>
       The file names are in hexadecimal.  There is no simple recipe such as
       the ones for other options of appending zeroes.
      </para>
+     <!-- 52352 = SLRU_PAGES_PER_SEGMENT * floor(BLCKSZ/20) * 4; see multixact.c -->
     </listitem>
    </varlistentry>
 
@@ -354,6 +358,7 @@ <title>Options</title>
       in <filename>pg_xact</filename>, <literal>-u 0x700000</literal> will work (five
       trailing zeroes provide the proper multiplier).
      </para>
+     <!-- 1048576 = SLRU_PAGES_PER_SEGMENT * BLCKSZ * CLOG_XACTS_PER_BYTE -->
     </listitem>
    </varlistentry>
 
@@ -375,6 +380,7 @@ <title>Options</title>
       in <filename>pg_xact</filename>, <literal>-x 0x1200000</literal> will work (five
       trailing zeroes provide the proper multiplier).
      </para>
+     <!-- 1048576 = SLRU_PAGES_PER_SEGMENT * BLCKSZ * CLOG_XACTS_PER_BYTE -->
     </listitem>
    </varlistentry>
   </variablelist>
diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c
index 47e05bd2c9..89b35c2748 100644
--- a/src/bin/pg_resetwal/pg_resetwal.c
+++ b/src/bin/pg_resetwal/pg_resetwal.c
@@ -211,6 +211,7 @@ main(int argc, char *argv[])
 					exit(1);
 				}
 
+				// FIXME: why 2?
 				if (set_oldest_commit_ts_xid < 2 &&
 					set_oldest_commit_ts_xid != 0)
 					pg_fatal("transaction ID (-c) must be either 0 or greater than or equal to 2");
-- 
2.42.0