the standard regression tests.  See <xref
     linkend="regress-run"/> for details on running the tests.
    </para>
   </listitem>
   <listitem>
    <para>
     File system or storage subsystem faults when data checksums are
     disabled.
    </para>
    <para>
     Note that <filename>amcheck</filename> examines a page as represented in some
     shared memory buffer at the time of verification if there is only a
     shared buffer hit when accessing the block. Consequently,
     <filename>amcheck</filename> does not necessarily examine data read from the
     file system at the time of verification. Note that when checksums are
     enabled, <filename>amcheck</filename> may raise an error due to a checksum
     failure when a corrupt block is read into a buffer.
    </para>
   </listitem>
   <listitem>
    <para>
     Corruption caused by faulty RAM, or the broader memory subsystem.
    </para>
    <para>
     <productname>PostgreSQL</productname> does not protect against correctable
     memory errors and it is assumed you will operate using RAM that
     uses industry standard Error Correcting Codes (ECC) or better
     protection.  However, ECC memory is typically only immune to
     single-bit errors, and should not be assumed to provide
     <emphasis>absolute</emphasis> protection against failures that
     result in memory corruption.
    </para>
    <para>
     When <parameter>heapallindexed</parameter> verification is
     performed, there is generally a greatly increased chance of
     detecting single-bit errors, since strict binary equality is
     tested, and the indexed attributes within the heap are tested.
    </para>
   </listitem>
  </itemizedlist>
 </para>

 <para>
  Structural corruption can happen due to faulty storage hardware, or
  relation files being overwritten or modified by unrelated software.
  This kind of corruption can also be detected with
  <link linkend="checksums"><application>data page
  checksums</application></link>.
 </para>

 <para>
  Relation pages which are correctly formatted, internally consistent, and
  correct relative to their own internal checksums may still contain
  logical