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Updates to reflect availability of autocommit option.

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Tom Lane 2002-08-30 22:45:25 +00:00
parent 26993b2918
commit 9c279355fb
2 changed files with 45 additions and 25 deletions
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47
doc/src/sgml/ref/begin.sgml
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@ -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>

23
doc/src/sgml/ref/start_transaction.sgml
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@ -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>