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

Author: david-rowley

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>
@@ -129,6 +130,19 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
     </listitem>
    </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>

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>
@@ -392,6 +393,19 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     </listitem>
    </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>

doc/src/sgml/ref/vacuumdb.sgml

@@ -121,6 +121,19 @@ PostgreSQL documentation
       </listitem>
      </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>
@@ -278,19 +291,6 @@ PostgreSQL documentation
       </listitem>
      </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>

src/bin/scripts/vacuumdb.c

@@ -1128,6 +1128,7 @@ help(const char *progname)
 	printf(_("  %s [OPTION]... [DBNAME]\n"), progname);
 	printf(_("\nOptions:\n"));
 	printf(_("  -a, --all                       vacuum all databases\n"));
+	printf(_("      --buffer-usage-limit=SIZE   size of ring buffer used for vacuum\n"));
 	printf(_("  -d, --dbname=DBNAME             database to vacuum\n"));
 	printf(_("      --disable-page-skipping     disable all page-skipping behavior\n"));
 	printf(_("  -e, --echo                      show the commands being sent to the server\n"));
@@ -1136,7 +1137,6 @@ help(const char *progname)
 	printf(_("      --force-index-cleanup       always remove index entries that point to dead tuples\n"));
 	printf(_("  -j, --jobs=NUM                  use this many concurrent connections to vacuum\n"));
 	printf(_("      --min-mxid-age=MXID_AGE     minimum multixact ID age of tables to vacuum\n"));
-	printf(_("      --buffer-usage-limit=BUFSIZE size of ring buffer used for vacuum\n"));
 	printf(_("      --min-xid-age=XID_AGE       minimum transaction ID age of tables to vacuum\n"));
 	printf(_("      --no-index-cleanup          don't remove index entries that point to dead tuples\n"));
 	printf(_("      --no-process-main           skip the main relation\n"));