With a recent commit truncate is transaction safe in 7.4.

Rod Taylor

doc/src/sgml/ref/truncate.sgml

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 PostgreSQL documentation
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@@ -84,12 +84,6 @@ TRUNCATE TABLE
    <command>DELETE</command> but since it does not actually scan the
    table it is faster. This is most useful on large tables.
   </para>
-
-  <para>
-   <command>TRUNCATE</command> cannot be executed inside a transaction
-   block (<command>BEGIN</>/<command>COMMIT</> pair), because there is
-   no way to roll it back.
-  </para>
  </refsect1>
 
  <refsect1 id="R1-SQL-TRUNCATE-2">