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Rethink the locking mechanisms used for CREATE/DROP/RENAME DATABASE.

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The former approach used ExclusiveLock on pg_database, which being a
cluster-wide lock meant only one of these operations could proceed at
a time; worse, it also blocked all incoming connections in ReverifyMyDatabase.
Now that we have LockSharedObject(), we can use locks of different types
applied to databases considered as objects.  This allows much more
flexible management of the interlocking: two CREATE DATABASEs need not
block each other, and need not block connections except to the template
database being used.  Similarly DROP DATABASE doesn't block unrelated
operations.  The locking used in flatfiles.c is also much narrower in
scope than before.  Per recent proposal.
This commit is contained in:
Tom Lane
2006-05-04 16:07:29 +00:00
parent cb98e6fb8f
commit 52667d56a3
9 changed files with 454 additions and 408 deletions
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23
doc/src/sgml/ref/create_database.sgml
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@@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_database.sgml,v 1.44 2005/07/31 17:19:17 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_database.sgml,v 1.45 2006/05/04 16:07:29 tgl Exp $
PostgreSQL documentation
-->
@@ -45,7 +45,7 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
<para>
Normally, the creator becomes the owner of the new database.
Superusers can create databases owned by other users using the
Superusers can create databases owned by other users, by using the
<literal>OWNER</> clause. They can even create databases owned by
users with no special privileges. Non-superusers with <literal>CREATEDB</>
privilege can only create databases owned by themselves.
@@ -104,7 +104,8 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
Character set encoding to use in the new database. Specify
a string constant (e.g., <literal>'SQL_ASCII'</literal>),
or an integer encoding number, or <literal>DEFAULT</literal>
to use the default encoding. The character sets supported by the
to use the default encoding (namely, the encoding of the
template database). The character sets supported by the
<productname>PostgreSQL</productname> server are described in
<xref linkend="multibyte-charset-supported">.
</para>
@@ -169,7 +170,11 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
Although it is possible to copy a database other than <literal>template1</>
by specifying its name as the template, this is not (yet) intended as
a general-purpose <quote><command>COPY DATABASE</command></quote> facility.
We recommend that databases used as templates be treated as read-only.
The principal limitation is that no other sessions can be connected to
the template database while it is being copied. <command>CREATE
DATABASE</> will fail if any other connection exists when it starts;
otherwise, new connections to the template database are locked out
until <command>CREATE DATABASE</> completes.
See <xref linkend="manage-ag-templatedbs"> for more information.
</para>
@@ -220,6 +225,16 @@ CREATE DATABASE music ENCODING 'LATIN1';
implementation-defined.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-alterdatabase" endterm="sql-alterdatabase-title"></member>
<member><xref linkend="sql-dropdatabase" endterm="sql-dropdatabase-title"></member>
</simplelist>
</refsect1>
</refentry>
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