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Read-only transactions, as defined in SQL.

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This commit is contained in:
Peter Eisentraut
2003-01-10 22:03:30 +00:00
parent b7ca9bdf18
commit b65cd56240
16 changed files with 427 additions and 146 deletions
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53
doc/src/sgml/ref/start_transaction.sgml
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@@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.3 2002/08/30 22:45:25 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/start_transaction.sgml,v 1.4 2003/01/10 22:03:27 petere Exp $
PostgreSQL documentation
-->
@@ -20,7 +20,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ]
START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
</synopsis>
<refsect2 id="R2-SQL-START-TRANSACTION-1">
@@ -77,52 +77,23 @@ WARNING: BEGIN: already a transaction in progress
<title>Description</title>
<para>
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
<xref linkend="sql-begin" endterm="sql-begin-title"> command.
This command begins a new transaction. If the isolation level or
read/write mode is specified, the new transaction has those
characteristics, as if <xref linkend="sql-set-transaction"
endterm="sql-set-transaction-title"> was executed. In all other
respects, the behavior of this command is identical to the <xref
linkend="sql-begin" endterm="sql-begin-title"> command.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<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 default isolation
level is used.
</para>
</refsect1>
<refsect1 id="R1-SQL-START-TRANSACTION-3">
<title>Compatibility</title>
<refsect2 id="R2-SQL-START-TRANSACTION-4">
<title>SQL99</title>
<para>
<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 lack of predicate
locking, the <option>SERIALIZABLE</option> level is
not truly serializable. See the <citetitle>User's Guide</citetitle>
for details.
</para>
<para>
In <acronym>SQL99</acronym> this statement can specify two other
properties of the new transaction: whether the transaction is
read-only and the size of the diagnostics area. Neither of these
concepts are currently supported in
<productname>PostgreSQL</productname>.
</para>
</refsect2>
<para>
SQL99; but see also the compatibility section of <xref
linkend="sql-set-transaction" endterm="sql-set-transaction-title">.
</para>
</refsect1>
</refentry>