From 96889392e915e5c77384d274db2a2c42b684c274 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Thu, 6 Nov 2003 22:08:15 +0000
Subject: Implement isolation levels read uncommitted and repeatable read as
 acting like the next higher one.

---
 doc/src/sgml/mvcc.sgml                  | 23 ++++++++++++++++++++---
 doc/src/sgml/ref/set_transaction.sgml   | 29 +++++++++++++++++------------
 doc/src/sgml/ref/start_transaction.sgml |  6 ++++--
 doc/src/sgml/runtime.sgml               | 12 +++++++-----
 4 files changed, 48 insertions(+), 22 deletions(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index e46c5928c78..a56d4a18a92 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/mvcc.sgml,v 2.40 2003/11/04 09:55:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/mvcc.sgml,v 2.41 2003/11/06 22:08:14 petere Exp $
 -->
 
  <chapter id="mvcc">
@@ -206,8 +206,25 @@ $Header: /cvsroot/pgsql/doc/src/sgml/mvcc.sgml,v 2.40 2003/11/04 09:55:38 petere
     </table>
 
    <para>
-    <productname>PostgreSQL</productname>
-    offers the Read Committed and Serializable isolation levels.
+    In <productname>PostgreSQL</productname>, you can use all four
+    possible transaction isolation levels.  Internally, there are only
+    two distinct isolation levels, which correspond to the levels Read
+    Committed and Serializable.  When you select the level Read
+    Uncommitted you really get Read Committed, and when you select
+    Repeatable Read you really get Serializable, so the actual
+    isolation level may be stricter than what you select.  This is
+    permitted by the SQL standard: the four isolation levels only
+    define which phenomena must not happen, they do not define which
+    phenomena must happen.  The reason that PostgreSQL only provides
+    two isolation levels is that this is the only sensible way to map
+    the isolation levels to the multiversion concurrency control
+    architecture.  The behavior of the available isolation levels is
+    detailed in the following subsections.
+   </para>
+
+   <para>
+    To set the transaction isolation level of a transaction, use the
+    command <xref linkend="sql-set-transaction">.
    </para>
 
   <sect2 id="xact-read-committed">
diff --git a/doc/src/sgml/ref/set_transaction.sgml b/doc/src/sgml/ref/set_transaction.sgml
index cbe41d7175f..809b884d6ba 100644
--- a/doc/src/sgml/ref/set_transaction.sgml
+++ b/doc/src/sgml/ref/set_transaction.sgml
@@ -1,4 +1,4 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.17 2003/09/11 21:42:20 momjian Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.18 2003/11/06 22:08:14 petere Exp $ -->
 <refentry id="SQL-SET-TRANSACTION">
  <refmeta>
   <refentrytitle id="SQL-SET-TRANSACTION-TITLE">SET TRANSACTION</refentrytitle>
@@ -17,9 +17,12 @@
  <refsynopsisdiv>
 <synopsis>
 SET TRANSACTION
-    [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
+    [ ISOLATION LEVEL { READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE } ]
+    [ READ WRITE | READ ONLY ]
+
 SET SESSION CHARACTERISTICS AS TRANSACTION
-    [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
+    [ ISOLATION LEVEL { READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE } ]
+    [ READ WRITE | READ ONLY ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -76,8 +79,11 @@ SET SESSION CHARACTERISTICS AS TRANSACTION
     </varlistentry>
    </variablelist>
 
-   The transaction isolation level cannot be set after the first query
-   or data-modification statement (<command>SELECT</command>,
+   The level <literal>READ UNCOMMITTED</literal> is mapped to
+   <literal>READ COMMITTED</literal>, the level <literal>REPEATABLE
+   READ</literal> is mapped to <literal>SERIALIZABLE</literal>, The
+   transaction isolation level cannot be set after the first query or
+   data-modification statement (<command>SELECT</command>,
    <command>INSERT</command>, <command>DELETE</command>,
    <command>UPDATE</command>, <command>FETCH</command>,
    <command>COPY</command>) of a transaction has been executed.  See
@@ -122,13 +128,12 @@ SET default_transaction_isolation = '<replaceable>value</replaceable>'
   <para>
    Both commands are defined in the <acronym>SQL</acronym> standard.
    <literal>SERIALIZABLE</literal> is the default transaction
-   isolation level in the standard; in <productname>PostgreSQL</productname> the default is
-   ordinarily <literal>READ COMMITTED</literal>, but you can change it as
-   described above.  <productname>PostgreSQL</productname> does not
-   provide the isolation levels <literal>READ UNCOMMITTED</literal>
-   and <literal>REPEATABLE READ</literal>. Because of multiversion
-   concurrency control, the <literal>SERIALIZABLE</literal> level is
-   not truly serializable. See <xref linkend="mvcc"> for details.
+   isolation level in the standard; in
+   <productname>PostgreSQL</productname> the default is ordinarily
+   <literal>READ COMMITTED</literal>, but you can change it as
+   described above.  Because of multiversion concurrency control, the
+   <literal>SERIALIZABLE</literal> level is not truly
+   serializable. See <xref linkend="mvcc"> for details.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/start_transaction.sgml b/doc/src/sgml/ref/start_transaction.sgml
index 60089d71ee9..7b1a2d58391 100644
--- a/doc/src/sgml/ref/start_transaction.sgml
+++ b/doc/src/sgml/ref/start_transaction.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.7 2003/09/09 18:28:53 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.8 2003/11/06 22:08:14 petere Exp $
 PostgreSQL documentation
 -->
 
@@ -20,7 +20,9 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
+START TRANSACTION
+    [ ISOLATION LEVEL { READ UNCOMMITTED | READ COMMITTED | REPEATABLE READ | SERIALIZABLE } ]
+    [ READ WRITE | READ ONLY ]
 </synopsis>
  </refsynopsisdiv>
 
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index e6a9478cbb1..d23c78d0cc5 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.216 2003/11/04 09:55:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.217 2003/11/06 22:08:14 petere Exp $
 -->
 
 <Chapter Id="runtime">
@@ -2043,10 +2043,12 @@ SET ENABLE_SEQSCAN TO OFF;
       <term><varname>default_transaction_isolation</varname> (<type>string</type>)</term>
       <listitem>
        <para>
-        Each SQL transaction has an isolation level, which can be either
-        <quote>read committed</quote> or <quote>serializable</quote>.
-        This parameter controls the default isolation level of each new
-        transaction. The default is <quote>read committed</quote>.
+        Each SQL transaction has an isolation level, which can be
+        either <quote>read uncommitted</quote>, <quote>read
+        committed</quote>, <quote>repeatable read</quote>, or
+        <quote>serializable</quote>.  This parameter controls the
+        default isolation level of each new transaction. The default
+        is <quote>read committed</quote>.
        </para>
 
        <para>
-- 
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