Improve VACUUM/ANALYZE BUFFER_USAGE_LIMIT docs

This addresses various deficiencies in the documentation for VACUUM and
ANALYZE's BUFFER_USEAGE_LIMIT docs.

Here we declare "size" in the syntax synopsis for VACUUM and ANALYZE's
BUFFER_USAGE_LIMIT option and then define exactly what values can be
specified for it in the section for that below.

Also, fix the incorrect ordering of vacuumdb options both in the documents
and in vacuumdb's --help output.  These should be in alphabetical order.

In passing also add the minimum/maximum range for the BUFFER_USAGE_LIMIT
option.  These will also serve as example values that can be modified and
used.

Reported-by: Peter Eisentraut
Discussion: https://postgr.es/m/16845cb1-b228-e157-f293-5892bced9253@enterprisedb.com

3 files changed, 45 insertions, 17 deletions

diff --git a/doc/src/sgml/ref/analyze.sgml b/doc/src/sgml/ref/analyze.sgml
index 94e30f1ce7..20c6f9939f 100644
--- a/doc/src/sgml/ref/analyze.sgml
+++ b/doc/src/sgml/ref/analyze.sgml
@@ -28,7 +28,7 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
 
     VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
     SKIP_LOCKED [ <replaceable class="parameter">boolean</replaceable> ]
-    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">string</replaceable> ]
+    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">size</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -110,7 +110,8 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
       <xref linkend="guc-vacuum-buffer-usage-limit"/>.  Higher settings can
       allow <command>ANALYZE</command> to run more quickly, but having too
       large a setting may cause too many other useful pages to be evicted from
-      shared buffers.
+      shared buffers.  The minimum value is <literal>128 kB</literal> and the
+      maximum value is <literal>16 GB</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -130,6 +131,19 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
    </varlistentry>
 
    <varlistentry>
+    <term><replaceable class="parameter">size</replaceable></term>
+    <listitem>
+     <para>
+      Specifies an amount of memory in kilobytes.  Sizes may also be specified
+      as a string containing the numerical size followed by any one of the
+      following memory units: <literal>kB</literal> (kilobytes),
+      <literal>MB</literal> (megabytes), <literal>GB</literal> (gigabytes), or
+      <literal>TB</literal> (terabytes).
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><replaceable class="parameter">table_name</replaceable></term>
     <listitem>
      <para>
diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index dd0fbb8cb7..57bc4c23ec 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/doc/src/sgml/ref/vacuum.sgml
@@ -39,7 +39,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     PARALLEL <replaceable class="parameter">integer</replaceable>
     SKIP_DATABASE_STATS [ <replaceable class="parameter">boolean</replaceable> ]
     ONLY_DATABASE_STATS [ <replaceable class="parameter">boolean</replaceable> ]
-    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">string</replaceable> ]
+    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">size</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -364,7 +364,8 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
       <xref linkend="guc-vacuum-buffer-usage-limit"/>.  Higher settings can
       allow <command>VACUUM</command> to run more quickly, but having too
       large a setting may cause too many other useful pages to be evicted from
-      shared buffers.
+      shared buffers.  The minimum value is <literal>128 kB</literal> and the
+      maximum value is <literal>16 GB</literal>.
      </para>
     </listitem>
    </varlistentry>
@@ -393,6 +394,19 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
    </varlistentry>
 
    <varlistentry>
+    <term><replaceable class="parameter">size</replaceable></term>
+    <listitem>
+     <para>
+      Specifies an amount of memory in kilobytes.  Sizes may also be specified
+      as a string containing the numerical size followed by any one of the
+      following memory units: <literal>kB</literal> (kilobytes),
+      <literal>MB</literal> (megabytes), <literal>GB</literal> (gigabytes), or
+      <literal>TB</literal> (terabytes).
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><replaceable class="parameter">table_name</replaceable></term>
     <listitem>
      <para>
diff --git a/doc/src/sgml/ref/vacuumdb.sgml b/doc/src/sgml/ref/vacuumdb.sgml
index 8280cf0fb0..caf97af215 100644
--- a/doc/src/sgml/ref/vacuumdb.sgml
+++ b/doc/src/sgml/ref/vacuumdb.sgml
@@ -122,6 +122,19 @@ PostgreSQL documentation
      </varlistentry>
 
      <varlistentry>
+      <term><option>--buffer-usage-limit <replaceable class="parameter">size</replaceable></option></term>
+      <listitem>
+       <para>
+        Specifies the
+        <glossterm linkend="glossary-buffer-access-strategy">Buffer Access Strategy</glossterm>
+        ring buffer size for a given invocation of <application>vacuumdb</application>.
+        This size is used to calculate the number of shared buffers which will
+        be reused as part of this strategy.  See <xref linkend="sql-vacuum"/>.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
       <term><option><optional>-d</optional> <replaceable class="parameter">dbname</replaceable></option></term>
       <term><option><optional>--dbname=</optional><replaceable class="parameter">dbname</replaceable></option></term>
       <listitem>
@@ -279,19 +292,6 @@ PostgreSQL documentation
      </varlistentry>
 
      <varlistentry>
-      <term><option>--buffer-usage-limit <replaceable class="parameter">buffer_usage_limit</replaceable></option></term>
-      <listitem>
-       <para>
-        Specifies the
-        <glossterm linkend="glossary-buffer-access-strategy">Buffer Access Strategy</glossterm>
-        ring buffer size for a given invocation of <application>vacuumdb</application>.
-        This size is used to calculate the number of shared buffers which will
-        be reused as part of this strategy.  See <xref linkend="sql-vacuum"/>.
-       </para>
-      </listitem>
-     </varlistentry>
-
-     <varlistentry>
       <term><option>-n <replaceable class="parameter">schema</replaceable></option></term>
       <term><option>--schema=<replaceable class="parameter">schema</replaceable></option></term>
       <listitem>