diff --git a/doc/src/sgml/ref/begin.sgml b/doc/src/sgml/ref/begin.sgml
index 850bfd77e68c98ec6884418bca6db0cff37d3fea..11ca82e6d49fd1a10fbef839e3b9683ddb156c66 100644
--- a/doc/src/sgml/ref/begin.sgml
+++ b/doc/src/sgml/ref/begin.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/begin.sgml,v 1.18 2002/08/04 04:31:44 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/begin.sgml,v 1.19 2002/08/30 22:45:25 tgl Exp $
PostgreSQL documentation
-->
@@ -103,33 +103,35 @@ WARNING: BEGIN: already a transaction in progress
<command>BEGIN</command> initiates a user transaction in chained mode,
i.e., all user statements after <command>BEGIN</command> command will
be executed in a single transaction until an explicit
- <xref linkend="sql-commit" endterm="sql-commit-title">,
- <xref linkend="sql-rollback" endterm="sql-rollback-title">,
- or execution abort. Statements in chained mode are executed much faster,
+ <xref linkend="sql-commit" endterm="sql-commit-title"> or
+ <xref linkend="sql-rollback" endterm="sql-rollback-title">.
+ Statements are executed more quickly in chained mode,
because transaction start/commit requires significant CPU and disk
activity. Execution of multiple statements inside a transaction
- is also required for consistency when changing several
- related tables.
+ is also useful to ensure consistency when changing several
+ related tables: other clients will be unable to see the intermediate
+ states wherein not all the related updates have been done.
</para>
<para>
The default transaction isolation level in
<productname>PostgreSQL</productname>
- is READ COMMITTED, where queries inside the transaction see only changes
- committed before query execution. So, you have to use
+ is READ COMMITTED, wherein each query inside the transaction sees changes
+ committed before that query begins execution. So, you have to use
<command>SET TRANSACTION ISOLATION LEVEL SERIALIZABLE</command>
- just after <command>BEGIN</command> if you need more rigorous transaction isolation.
+ just after <command>BEGIN</command> if you need more rigorous transaction
+ isolation. (Alternatively, you can change the default transaction
+ isolation level; see the <citetitle>PostgreSQL Administrator's
+ Guide</citetitle> for details.)
In SERIALIZABLE mode queries will see only changes committed before
the entire
transaction began (actually, before execution of the first DML statement
- in a serializable transaction).
+ in the transaction).
</para>
<para>
- If the transaction is committed, <productname>PostgreSQL</productname>
- will ensure either that all updates are done or else that none of
- them are done. Transactions have the standard <acronym>ACID</acronym>
- (atomic, consistent, isolatable, and durable) property.
+ Transactions have the standard <acronym>ACID</acronym>
+ (atomic, consistent, isolatable, and durable) properties.
</para>
<refsect2 id="R2-SQL-BEGIN-3">
@@ -140,9 +142,9 @@ WARNING: BEGIN: already a transaction in progress
Notes
</title>
<para>
- Refer to <xref linkend="sql-lock" endterm="sql-lock-title">
- for further information
- about locking tables inside a transaction.
+ <xref linkend="sql-start-transaction"
+ endterm="sql-start-transaction-title"> has the same functionality
+ as <command>BEGIN</>.
</para>
<para>
@@ -151,6 +153,17 @@ WARNING: BEGIN: already a transaction in progress
<xref linkend="SQL-ROLLBACK" endterm="SQL-ROLLBACK-TITLE">
to terminate a transaction.
</para>
+
+ <para>
+ Refer to <xref linkend="sql-lock" endterm="sql-lock-title">
+ for further information
+ about locking tables inside a transaction.
+ </para>
+
+ <para>
+ If you turn <literal>autocommit</> mode off, then <command>BEGIN</>
+ is not required: any SQL command automatically starts a transaction.
+ </para>
</refsect2>
</refsect1>
diff --git a/doc/src/sgml/ref/start_transaction.sgml b/doc/src/sgml/ref/start_transaction.sgml
index 2e657c610bbe569ba5c9982344352ac34a4bf373..fb8dd1319322a6e2074583b8b3af49c9b9bb265c 100644
--- a/doc/src/sgml/ref/start_transaction.sgml
+++ b/doc/src/sgml/ref/start_transaction.sgml
@@ -1,4 +1,8 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.2 2002/08/06 05:32:16 momjian Exp $ -->
+<!--
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.3 2002/08/30 22:45:25 tgl Exp $
+PostgreSQL documentation
+-->
+
<refentry id="SQL-START-TRANSACTION">
<docinfo>
<date>2002-07-26</date>
@@ -76,7 +80,7 @@ WARNING: BEGIN: already a transaction in progress
This command begins a new transaction. If the isolation level is
specified, the new transaction has that isolation level. In all other
respects, the behavior of this command is identical to the
- <command>BEGIN</command> command.
+ <xref linkend="sql-begin" endterm="sql-begin-title"> command.
</para>
</refsect1>
@@ -87,8 +91,8 @@ WARNING: BEGIN: already a transaction in progress
<para>
The isolation level of a transaction can also be set with the <xref
linkend="sql-set-transaction" endterm="sql-set-transaction-title">
- command. If no isolation level is specified, the level defaults to
- <option>READ COMMITTED</option>.
+ command. If no isolation level is specified, the default isolation
+ level is used.
</para>
</refsect1>
@@ -99,11 +103,14 @@ WARNING: BEGIN: already a transaction in progress
<title>SQL99</title>
<para>
- <option>SERIALIZABLE</option> is the default level in
- <acronym>SQL</acronym>. <productname>PostgreSQL</productname>
+ <option>SERIALIZABLE</option> is the default isolation level in
+ <acronym>SQL99</acronym>, but it is not the usual default in
+ <productname>PostgreSQL</productname>: the factory default setting
+ is READ COMMITTED.
+ <productname>PostgreSQL</productname>
does not provide the isolation levels <option>READ UNCOMMITTED</option>
- and <option>REPEATABLE READ</option>. Because of multiversion
- concurrency control, the <option>SERIALIZABLE</option> level is
+ and <option>REPEATABLE READ</option>. Because of lack of predicate
+ locking, the <option>SERIALIZABLE</option> level is
not truly serializable. See the <citetitle>User's Guide</citetitle>
for details.
</para>