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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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28
doc/src/sgml/features.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.13 2003/01/10 11:02:41 petere Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.14 2003/01/10 22:03:26 petere Exp $
-->
<appendix id="features">
@ -642,6 +642,12 @@ $Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.13 2003/01/10 11:02:41 pe
<entry>ROLLBACK statement</entry>
<entry></entry>
</row>
<row>
<entry>E152</entry>
<entry>Core</entry>
<entry>Basic SET TRANSACTION statement</entry>
<entry></entry>
</row>
<row>
<entry>E152-01</entry>
<entry>Core</entry>
@ -649,6 +655,13 @@ $Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.13 2003/01/10 11:02:41 pe
clause</entry>
<entry></entry>
</row>
<row>
<entry>E152-02</entry>
<entry>Core</entry>
<entry>SET TRANSACTION statement: READ ONLY and READ WRITE
clauses</entry>
<entry></entry>
</row>
<row>
<entry>E161</entry>
<entry>Core</entry>
@ -1598,19 +1611,6 @@ $Header: /cvsroot/pgsql/doc/src/sgml/features.sgml,v 2.13 2003/01/10 11:02:41 pe
<entry>WITH HOLD cursors</entry>
<entry>Cursor to stay open across transactions</entry>
</row>
<row>
<entry>E152</entry>
<entry>Core</entry>
<entry>Basic SET TRANSACTION statement</entry>
<entry></entry>
</row>
<row>
<entry>E152-02</entry>
<entry>Core</entry>
<entry>SET TRANSACTION statement: READ ONLY and READ WRITE
clauses</entry>
<entry>Syntax accepted; READ ONLY not supported</entry>
</row>
<row>
<entry>E153</entry>
<entry>Core</entry>

70
doc/src/sgml/ref/set_transaction.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.9 2002/08/04 04:31:44 momjian Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.10 2003/01/10 22:03:27 petere Exp $ -->
<refentry id="SQL-SET-TRANSACTION">
<docinfo>
<date>2000-11-24</date>
@ -16,9 +16,10 @@
<refsynopsisdiv>
<synopsis>
SET TRANSACTION ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE }
SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
{ READ COMMITTED | SERIALIZABLE }
SET TRANSACTION
[ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
SET SESSION CHARACTERISTICS AS TRANSACTION
[ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
</synopsis>
</refsynopsisdiv>
@ -26,17 +27,19 @@ SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
<title>Description</title>
<para>
This command sets the transaction isolation level. The
<command>SET TRANSACTION</command> command sets the characteristics
for the current SQL-transaction. It has no effect on any subsequent
transactions. This command cannot be used 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. <command>SET SESSION CHARACTERISTICS</command>
sets the default transaction isolation level for each transaction
for a session. <command>SET TRANSACTION</command> can override it
for an individual transaction.
The <command>SET TRANSACTION</command> command sets the transaction
characteristics of the current SQL-transaction. It has no effect on
any subsequent transactions. <command>SET SESSION
CHARACTERISTICS</command> sets the default transaction
characteristics for each transaction of a session. <command>SET
TRANSACTION</command> can override it for an individual
transaction.
</para>
<para>
The available transaction characteristics are the transaction
isolation level and the transaction access mode (read/write or
read-only).
</para>
<para>
@ -45,7 +48,7 @@ SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
<variablelist>
<varlistentry>
<term>READ COMMITTED</term>
<term><literal>READ COMMITTED<literal></term>
<listitem>
<para>
A statement can only see rows committed before it began. This
@ -55,7 +58,7 @@ SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
</varlistentry>
<varlistentry>
<term>SERIALIZABLE</term>
<term><literal>SERIALIZABLE</literal></term>
<listitem>
<para>
The current transaction can only see rows committed before
@ -72,6 +75,28 @@ SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
</listitem>
</varlistentry>
</variablelist>
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.
</para>
<para>
The transaction access mode determines whether the transaction is
read/write or read-only. Read/write is the default. When a
transaction is read-only, the following SQL commands are
disallowed: <literal>INSERT</literal>, <literal>UPDATE</literal>,
<literal>DELETE</literal>, and <literal>COPY TO</literal> if the
table they would write to is not a temporary table; all
<literal>CREATE</literal>, <literal>ALTER</literal>, and
<literal>DROP</literal> commands; <literal>COMMENT</literal>,
<literal>GRANT</literal>, <literal>REVOKE</literal>,
<literal>TRUNCATE</literal>; and <literal>EXPLAIN ANALYZE</literal>
and <literal>EXECUTE</literal> if the command they would execute is
among those listed. This is a high-level notion of read-only that
does not prevent writes to disk.
</para>
</refsect1>
@ -97,7 +122,7 @@ SET default_transaction_isolation = '<replaceable>value</replaceable>'
<title>SQL92, SQL99</title>
<para>
<option>SERIALIZABLE</option> is the default level in
<option>SERIALIZABLE</option> is the default transaction isolation level in
<acronym>SQL</acronym>. <productname>PostgreSQL</productname> does
not provide the isolation levels <option>READ UNCOMMITTED</option>
and <option>REPEATABLE READ</option>. Because of multiversion
@ -107,11 +132,10 @@ SET default_transaction_isolation = '<replaceable>value</replaceable>'
</para>
<para>
In <acronym>SQL</acronym> there are two other transaction
characteristics that can be set with these commands: whether the
transaction is read-only and the size of the diagnostics area.
Neither of these concepts are supported in
<productname>PostgreSQL</productname>.
In <acronym>SQL</acronym> there is one other transaction
characteristic that can be set with these commands: the size of
the diagnostics area. This concept is not supported in
<productname>PostgreSQL</productname>.
</para>
</refsect2>
</refsect1>

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>

3
doc/src/sgml/release.sgml
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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.176 2003/01/08 00:22:26 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.177 2003/01/10 22:03:26 petere Exp $
-->
<appendix id="release">
@ -36,6 +36,7 @@ System can use either hash- or sort-based strategy for grouped aggregation
ON COMMIT options for temp tables
extra_float_digits option allows pg_dump to dump float data accurately
Long options for psql and pg_dump are now available on all platforms
Read-only transactions
]]></literallayout>
</sect1>