A table operates in one of three persistence modes (default, [temporary], and [unlogged]) described in [Chapter 28]. --point to the intro page for the chapter as expanded as below, not the reliability page.
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 05e2a8f8be..102cfeca68 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -5,8 +5,17 @@
<para>
This chapter explains how to control the reliability of
- <productname>PostgreSQL</productname>, including details about the
- Write-Ahead Log.
+ <productname>PostgreSQL</productname>. At its core this
+ involves writing all changes to disk twice - first to a
+ journal of changes called the write-ahead-log (WAL) and
+ then to the physical pages that comprise permanent tables
+ on disk (heap). This results in four high-level
+ <term>persistence modes</term> for tables.
+ The default mode results in both these features being
+ enabled. Temporary tables forgo both of these options,
+ while unlogged tables only forgo WAL. There is no WAL-only
+ operating mode. The rest of this chapter discusses
+ implementation details related to these two options.
</para>
David J.