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体验新版 GitCode,发现更多精彩内容 >>
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fb4f5f7c
编写于
6月 03, 1999
作者:
V
Vadim B. Mikheev
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差异文件
Notes in Migration to v6.5 section.
上级
9680a712
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2
隐藏空白更改
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+57
-3
doc/src/sgml/mvcc.sgml
doc/src/sgml/mvcc.sgml
+1
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doc/src/sgml/release.sgml
doc/src/sgml/release.sgml
+56
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未找到文件。
doc/src/sgml/mvcc.sgml
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...
@@ -515,7 +515,7 @@ ERROR: Can't serialize access due to concurrent update
...
@@ -515,7 +515,7 @@ ERROR: Can't serialize access due to concurrent update
by <command>SELECT</command> it doesn't mean that this row really
by <command>SELECT</command> it doesn't mean that this row really
exists at the time it is returned (i.e. sometime after the
exists at the time it is returned (i.e. sometime after the
statement or transaction began) nor
statement or transaction began) nor
that the row is protected from deletion or updat
e
by concurrent
that the row is protected from deletion or updat
ion
by concurrent
transactions before the current transaction does a commit or rollback.
transactions before the current transaction does a commit or rollback.
</para>
</para>
...
...
doc/src/sgml/release.sgml
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fb4f5f7c
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@@ -132,11 +132,65 @@
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@@ -132,11 +132,65 @@
is required for those wishing to migrate data from any
is required for those wishing to migrate data from any
previous release of <productname>Postgres</productname>.
previous release of <productname>Postgres</productname>.
</para>
</para>
</sect2>
<para>
Because readers in 6.5 don't lock data, regardless of transaction
isolation level, data read by one transaction can be overwritten by
another. In the other words, if a row is returned by
<command>SELECT</command> it doesn't mean that this row really exists
at the time it is returned (i.e. sometime after the statement or
transaction began) nor that the row is protected from deletion or
updation by concurrent transactions before the current transaction does
a commit or rollback.
</para>
<para>
To ensure the actual existance of a row and protect it against
concurrent updates one must use <command>SELECT FOR UPDATE</command> or
an appropriate <command>LOCK TABLE</command> statement. This should be
taken into account when porting applications from previous releases of
<productname>Postgres</productname> and other environments.
</para>
<para>
Keep above in mind if you are using contrib/refint.* triggers for
referential integrity. Additional technics are required now. One way is
to use <command>LOCK parent_table IN SHARE ROW EXCLUSIVE MODE</command>
command if a transaction is going to update/delete a primary key and
use <command>LOCK parent_table IN SHARE MODE</command> command if a
transaction is going to update/insert a foreign key.
<note>
<para>
Note that if you run a transaction in SERIALIZABLE mode then you must
execute <command>LOCK</command> commands above before execution of any
DML statement
(<command>SELECT/INSERT/DELETE/UPDATE/FETCH/COPY_TO</command>) in the
transaction.
</para>
</note>
<para>
These inconveniences will disappear when the ability to read durty
(uncommitted) data, regardless of isolation level, and true referential
integrity will be implemented.
</para>
</para>
</sect2>
<sect2>
<sect2>
<title>Detailed Change List</title>
<title>Detailed Change List</title>
<para>
<para>
<programlisting>
<programlisting>
Bug Fixes
Bug Fixes
...
...
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