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Minor editorializing.

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This commit is contained in:
Tom Lane 2004-08-14 22:17:08 +00:00
parent 3ea6d6d4d5
commit 11d8138ca3
1 changed files with 10 additions and 17 deletions
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doc/src/sgml/ref/set_transaction.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.20 2004/08/12 21:00:22 tgl Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/ref/set_transaction.sgml,v 1.21 2004/08/14 22:17:08 tgl Exp $ -->
<refentry id="SQL-SET-TRANSACTION"> <refentry id="SQL-SET-TRANSACTION">
<refmeta> <refmeta>
<refentrytitle id="SQL-SET-TRANSACTION-TITLE">SET TRANSACTION</refentrytitle> <refentrytitle id="SQL-SET-TRANSACTION-TITLE">SET TRANSACTION</refentrytitle>
@ -34,9 +34,9 @@ where <replaceable class="parameter">transaction_mode</replaceable> is one of:
characteristics of the current transaction. It has no effect on any characteristics of the current transaction. It has no effect on any
subsequent transactions. <command>SET SESSION subsequent transactions. <command>SET SESSION
CHARACTERISTICS</command> sets the default transaction CHARACTERISTICS</command> sets the default transaction
characteristics for subsequent transactions of a session. <command>SET characteristics for subsequent transactions of a session. These
TRANSACTION</command> can override it for an individual defaults can be overridden by <command>SET TRANSACTION</command> for an
transaction. individual transaction.
</para> </para>
<para> <para>
@ -68,14 +68,6 @@ where <replaceable class="parameter">transaction_mode</replaceable> is one of:
before the first query or data-modification statement was executed in before the first query or data-modification statement was executed in
this transaction. this transaction.
</para> </para>
<tip>
<para>
Intuitively, serializable means that two concurrent
transactions will leave the database in the same state as if
the two had been executed strictly one after the other (in one
order or the other).
</para>
</tip>
</listitem> </listitem>
</varlistentry> </varlistentry>
</variablelist> </variablelist>
@ -111,7 +103,7 @@ where <replaceable class="parameter">transaction_mode</replaceable> is one of:
<literal>TRUNCATE</literal>; and <literal>EXPLAIN ANALYZE</literal> <literal>TRUNCATE</literal>; and <literal>EXPLAIN ANALYZE</literal>
and <literal>EXECUTE</literal> if the command they would execute is and <literal>EXECUTE</literal> if the command they would execute is
among those listed. This is a high-level notion of read-only that among those listed. This is a high-level notion of read-only that
does not prevent writes to disk. does not prevent all writes to disk.
</para> </para>
</refsect1> </refsect1>
@ -138,8 +130,9 @@ where <replaceable class="parameter">transaction_mode</replaceable> is one of:
and <xref linkend="guc-default-transaction-read-only">. and <xref linkend="guc-default-transaction-read-only">.
(In fact <command>SET SESSION CHARACTERISTICS</command> is just a (In fact <command>SET SESSION CHARACTERISTICS</command> is just a
verbose equivalent for setting these variables with <command>SET</>.) verbose equivalent for setting these variables with <command>SET</>.)
This allows them to be set in the configuration file. Consult <xref This means the defaults can be set in the configuration file, via
linkend="runtime-config"> for more information. <command>ALTER DATABASE</>, etc. Consult <xref linkend="runtime-config">
for more information.
</para> </para>
</refsect1> </refsect1>
@ -149,10 +142,10 @@ where <replaceable class="parameter">transaction_mode</replaceable> is one of:
<para> <para>
Both commands are defined in the <acronym>SQL</acronym> standard. Both commands are defined in the <acronym>SQL</acronym> standard.
<literal>SERIALIZABLE</literal> is the default transaction <literal>SERIALIZABLE</literal> is the default transaction
isolation level in the standard; in isolation level in the standard. In
<productname>PostgreSQL</productname> the default is ordinarily <productname>PostgreSQL</productname> the default is ordinarily
<literal>READ COMMITTED</literal>, but you can change it as <literal>READ COMMITTED</literal>, but you can change it as
mentioned above. Because of multiversion concurrency control, the mentioned above. Because of lack of predicate locking, the
<literal>SERIALIZABLE</literal> level is not truly <literal>SERIALIZABLE</literal> level is not truly
serializable. See <xref linkend="mvcc"> for details. serializable. See <xref linkend="mvcc"> for details.
</para> </para>