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Commit52667d5

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Rethink the locking mechanisms used for CREATE/DROP/RENAME DATABASE.
The former approach used ExclusiveLock on pg_database, which being acluster-wide lock meant only one of these operations could proceed ata time; worse, it also blocked all incoming connections in ReverifyMyDatabase.Now that we have LockSharedObject(), we can use locks of different typesapplied to databases considered as objects. This allows much moreflexible management of the interlocking: two CREATE DATABASEs need notblock each other, and need not block connections except to the templatedatabase being used. Similarly DROP DATABASE doesn't block unrelatedoperations. The locking used in flatfiles.c is also much narrower inscope than before. Per recent proposal.
1 parentcb98e6f commit52667d5

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9 files changed

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-405
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9 files changed

+451
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‎doc/src/sgml/manage-ag.sgml

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@@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.45 2006/03/10 19:10:48 momjian Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/manage-ag.sgml,v 2.46 2006/05/04 16:07:28 tgl Exp $ -->
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<chapter id="managing-databases">
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<title>Managing Databases</title>
@@ -166,6 +166,7 @@ CREATE DATABASE <replaceable>dbname</> OWNER <replaceable>rolename</>;
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<programlisting>
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createdb -O <replaceable>rolename</> <replaceable>dbname</>
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</programlisting>
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from the shell.
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You must be a superuser to be allowed to create a database for
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someone else (that is, for a role you are not a member of).
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</para>
@@ -220,19 +221,15 @@ createdb -T template0 <replaceable>dbname</>
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<para>
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It is possible to create additional template databases, and indeed
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onemight copy any database in a cluster by specifying its name
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onemay copy any database in a cluster by specifying its name
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as the template for <command>CREATE DATABASE</>. It is important to
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understand, however, that this is not (yet) intended as
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a general-purpose <quote><command>COPY DATABASE</command></quote> facility. In particular, it is
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essential that the source database be idle (no data-altering transactions
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in progress)
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for the duration of the copying operation. <command>CREATE DATABASE</>
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will check
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that no session (other than itself) is connected to
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the source database at the start of the operation, but this does not
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guarantee that changes cannot be made while the copy proceeds, which
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would result in an inconsistent copied database. Therefore,
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we recommend that databases used as templates be treated as read-only.
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a general-purpose <quote><command>COPY DATABASE</command></quote> facility.
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The principal limitation is that no other sessions can be connected to
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the source database while it is being copied. <command>CREATE
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DATABASE</> will fail if any other connection exists when it starts;
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otherwise, new connections to the source database are locked out
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until <command>CREATE DATABASE</> completes.
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</para>
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<para>

‎doc/src/sgml/ref/create_database.sgml

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Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/create_database.sgml,v 1.44 2005/07/31 17:19:17 tgl Exp $
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$PostgreSQL: pgsql/doc/src/sgml/ref/create_database.sgml,v 1.45 2006/05/04 16:07:29 tgl Exp $
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PostgreSQL documentation
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-->
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@@ -45,7 +45,7 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
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<para>
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Normally, the creator becomes the owner of the new database.
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Superusers can create databases owned by other users using the
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Superusers can create databases owned by other users, by using the
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<literal>OWNER</> clause. They can even create databases owned by
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users with no special privileges. Non-superusers with <literal>CREATEDB</>
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privilege can only create databases owned by themselves.
@@ -104,7 +104,8 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
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Character set encoding to use in the new database. Specify
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a string constant (e.g., <literal>'SQL_ASCII'</literal>),
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or an integer encoding number, or <literal>DEFAULT</literal>
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to use the default encoding. The character sets supported by the
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to use the default encoding (namely, the encoding of the
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template database). The character sets supported by the
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<productname>PostgreSQL</productname> server are described in
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<xref linkend="multibyte-charset-supported">.
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</para>
@@ -169,7 +170,11 @@ CREATE DATABASE <replaceable class="PARAMETER">name</replaceable>
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Although it is possible to copy a database other than <literal>template1</>
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by specifying its name as the template, this is not (yet) intended as
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a general-purpose <quote><command>COPY DATABASE</command></quote> facility.
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We recommend that databases used as templates be treated as read-only.
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The principal limitation is that no other sessions can be connected to
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the template database while it is being copied. <command>CREATE
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DATABASE</> will fail if any other connection exists when it starts;
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otherwise, new connections to the template database are locked out
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until <command>CREATE DATABASE</> completes.
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See <xref linkend="manage-ag-templatedbs"> for more information.
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</para>
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@@ -220,6 +225,16 @@ CREATE DATABASE music ENCODING 'LATIN1';
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implementation-defined.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterdatabase" endterm="sql-alterdatabase-title"></member>
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<member><xref linkend="sql-dropdatabase" endterm="sql-dropdatabase-title"></member>
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</simplelist>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file

‎doc/src/sgml/ref/drop_database.sgml

Lines changed: 2 additions & 2 deletions
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@@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/drop_database.sgml,v 1.21 2005/11/22 15:24:17 adunstan Exp $
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$PostgreSQL: pgsql/doc/src/sgml/ref/drop_database.sgml,v 1.22 2006/05/04 16:07:29 tgl Exp $
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PostgreSQL documentation
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-->
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@@ -86,7 +86,7 @@ DROP DATABASE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
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<title>Compatibility</title>
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<para>
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The is no <command>DROP DATABASE</command> statement in the SQL standard.
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There is no <command>DROP DATABASE</command> statement in the SQL standard.
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</para>
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</refsect1>
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‎src/backend/catalog/pg_shdepend.c

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@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/catalog/pg_shdepend.c,v 1.8 2006/03/05 15:58:23 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/catalog/pg_shdepend.c,v 1.9 2006/05/04 16:07:29 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -37,7 +37,6 @@
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#include"lib/stringinfo.h"
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#include"miscadmin.h"
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#include"utils/fmgroids.h"
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#include"utils/inval.h"
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#include"utils/syscache.h"
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@@ -911,12 +910,6 @@ shdepLockAndCheckObject(Oid classId, Oid objectId)
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/* AccessShareLock should be OK, since we are not modifying the object */
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LockSharedObject(classId,objectId,0,AccessShareLock);
913912

914-
/*
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* We have to recognize sinval updates here, else our local syscache may
916-
* still contain the object even if it was just dropped.
917-
*/
918-
AcceptInvalidationMessages();
919-
920913
switch (classId)
921914
{
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caseAuthIdRelationId:

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