Clean up some obsolete statements about GiST indexes, and add a section

documenting GiST crash recovery procedures, as requested some time ago
by Teodor.  (The GiST chapter doesn't seem quite the right place for
the latter, but I'm not sure what else to do with it.)

doc/src/sgml/gist.sgml

@@ -1,11 +1,11 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.22 2005/10/21 01:41:28 tgl Exp $
 -->
 
 <chapter id="GiST">
 <title>GiST Indexes</title>
 
-<sect1 id="intro">
+<sect1 id="gist-intro">
  <title>Introduction</title>
 
  <para>
@@ -44,7 +44,7 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp
 
 </sect1>
 
-<sect1 id="extensibility">
+<sect1 id="gist-extensibility">
  <title>Extensibility</title>
 
  <para>
@@ -92,7 +92,7 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp
 
 </sect1>
 
-<sect1 id="implementation">
+<sect1 id="gist-implementation">
  <title>Implementation</title>
  
  <para>
@@ -180,19 +180,24 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp
 
 </sect1>
 
-<sect1 id="examples">
+<sect1 id="gist-examples">
  <title>Examples</title>
 
  <para>
-  To see example implementations of index methods implemented using
-  <acronym>GiST</acronym>, examine the following contrib modules:
+  The <productname>PostgreSQL</productname> source distribution includes
+  several examples of index methods implemented using
+  <acronym>GiST</acronym>.  The core system currently provides R-Tree
+  equivalent functionality for some of the built-in geometric datatypes
+  (see <filename>src/backend/access/gist/gistproc.c</>).  The following
+  <filename>contrib</> modules also contain <acronym>GiST</acronym>
+  operator classes: 
  </para>
  
  <variablelist>
   <varlistentry>
    <term>btree_gist</term>
    <listitem>
-    <para>B-Tree</para>
+    <para>B-Tree equivalent functionality for several datatypes</para>
    </listitem>
   </varlistentry>
 
@@ -213,26 +218,26 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp
   <varlistentry>
    <term>ltree</term>
    <listitem>
-    <para>Indexing for tree-like stuctures</para>
+    <para>Indexing for tree-like structures</para>
    </listitem>
   </varlistentry>
 
   <varlistentry>
-   <term>rtree_gist</term>
+   <term>pg_trgm</term>
    <listitem>
-    <para>R-Tree</para>
+    <para>Text similarity using trigram matching</para>
    </listitem>
   </varlistentry>
 
   <varlistentry>
    <term>seg</term>
    <listitem>
-    <para>Storage and indexed access for <quote>float ranges</quote></para>
+    <para>Indexing for <quote>float ranges</quote></para>
    </listitem>
   </varlistentry>
 
   <varlistentry>
-   <term>tsearch and tsearch2</term>
+   <term>tsearch2</term>
    <listitem>
     <para>Full text indexing</para>
    </listitem>
@@ -241,4 +246,33 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.21 2005/07/02 20:08:27 momjian Exp
 
 </sect1>
 
+<sect1 id="gist-recovery">
+ <title>Crash Recovery</title>
+
+ <para>
+  Usually, replay of the WAL log is sufficient to restore the integrity
+  of a GiST index following a database crash.  However, there are some
+  corner cases in which the index state is not fully rebuilt.  The index
+  will still be functionally correct, but there may be some performance
+  degradation.  When this occurs, the index can be repaired by
+  <command>VACUUM</>ing its table, or by rebuilding the index using
+  <command>REINDEX</>.  In some cases a plain <command>VACUUM</> is
+  not sufficient, and either <command>VACUUM FULL</> or <command>REINDEX</>
+  is needed.  The need for one of these procedures is indicated by occurrence
+  of this log message during crash recovery:
+<programlisting>
+LOG:  index NNN/NNN/NNN needs VACUUM or REINDEX to finish crash recovery
+</programlisting>
+  or this log message during routine index insertions:
+<programlisting>
+LOG:  index "FOO" needs VACUUM or REINDEX to finish crash recovery
+</programlisting>
+  If a plain <command>VACUUM</> finds itself unable to complete recovery
+  fully, it will return a notice:
+<programlisting>
+NOTICE:  index "FOO" needs VACUUM FULL or REINDEX to finish crash recovery
+</programlisting>
+ </para>
+</sect1>
+
 </chapter>