Add contrib/amcheck debug message.

Add a DEBUG1 message indicating that verification of the index structure
is underway.  Also reduce the severity level of the existing "tree
level" debug message to DEBUG1.  It should never have been made DEBUG2.
Any B-Tree index with more than a couple of levels will generally also
have so many pages that the per-page DEBUG2 messages will become
completely unmanageable.

In passing, add a new "Tip" to the docs that advises users that run into
corruption that the debug messages might provide useful additional
context.

1 files changed, 21 insertions, 0 deletions

diff --git a/doc/src/sgml/amcheck.sgml b/doc/src/sgml/amcheck.sgml
index c912d2aa895..58b163a3d94 100644
--- a/doc/src/sgml/amcheck.sgml
+++ b/doc/src/sgml/amcheck.sgml
@@ -166,6 +166,27 @@ ORDER BY c.relpages DESC LIMIT 10;
     </listitem>
    </varlistentry>
   </variablelist>
+  <tip>
+   <para>
+    <function>bt_index_parent_check</function> and
+    <function>bt_index_parent_check</function> both output log
+    messages about the verification process at
+    <literal>DEBUG1</literal> and <literal>DEBUG2</literal> severity
+    levels.  These messages provide detailed information about the
+    verification process that may be of interest to
+    <productname>PostgreSQL</productname> developers.  Advanced users
+    may also find this information helpful, since it provides
+    additional context should verification actually detect an
+    inconsistency.  Running:
+<programlisting>
+SET client_min_messages = DEBUG1;
+</programlisting>
+    in an interactive <application>psql</application> session before
+    running a verification query will display messages about the
+    progress of verification with a manageable level of detail.
+   </para>
+  </tip>
+
  </sect2>
 
  <sect2>