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pg_upgrade: Preserve database OIDs.

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Commit 9a974cbcba arranged to preserve
relfilenodes and tablespace OIDs. For similar reasons, also arrange
to preserve database OIDs.

One problem is that, up until now, the OIDs assigned to the template0
and postgres databases have not been fixed. This could be a problem
when upgrading, because pg_upgrade might try to migrate a database
from the old cluster to the new cluster while keeping the OID and find
a different database with that OID, resulting in a failure. If it finds
a database with the same name and the same OID that's OK: it will be
dropped and recreated. But the same OID and a different name is a
problem.

To prevent that, fix the OIDs for postgres and template0 to specific
values less than 16384. To avoid running afoul of this rule, these
values should not be changed in future releases. It's not a problem
that these OIDs aren't fixed in existing releases, because the OIDs
that we're assigning here weren't used for either of these databases
in any previous release. Thus, there's no chance that an upgrade of
a cluster from any previous release will collide with the OIDs we're
assigning here. And going forward, the OIDs will always be fixed, so
the only potential collision is with a system database having the
same name and the same OID, which is OK.

This patch lets users assign a specific OID to a database as well,
provided however that it can't be less than 16384. I (rhaas) thought
it might be better not to expose this capability to users, but the
consensus was otherwise, so the syntax is documented. Letting users
assign OIDs below 16384 would not be OK, though, because a
user-created database with a low-numbered OID might collide with a
system-created database in a future release. We therefore prohibit
that.

Shruthi KC, based on an earlier patch from Antonin Houska, reviewed
and with some adjustments by me.

Discussion: http://postgr.es/m/CA+TgmoYgTwYcUmB=e8+hRHOFA0kkS6Kde85+UNdon6q7bt1niQ@mail.gmail.com
Discussion: http://postgr.es/m/CAASxf_Mnwm1Dh2vd5FAhVX6S1nwNSZUB1z12VddYtM++H2+p7w@mail.gmail.com
This commit is contained in:
Robert Haas
2022-01-24 14:23:15 -05:00
parent 4f0bcc7350
commit aa01051418
11 changed files with 120 additions and 22 deletions
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18
doc/src/sgml/ref/create_database.sgml
View File

@ -31,7 +31,8 @@ CREATE DATABASE <replaceable class="parameter">name</replaceable>
[ TABLESPACE [=] <replaceable class="parameter">tablespace_name</replaceable> ]
[ ALLOW_CONNECTIONS [=] <replaceable class="parameter">allowconn</replaceable> ]
[ CONNECTION LIMIT [=] <replaceable class="parameter">connlimit</replaceable> ]
[ IS_TEMPLATE [=] <replaceable class="parameter">istemplate</replaceable> ] ]
[ IS_TEMPLATE [=] <replaceable class="parameter">istemplate</replaceable> ]
[ OID [=] <replaceable class="parameter">oid</replaceable> ] ]
</synopsis>
</refsynopsisdiv>
@ -203,6 +204,21 @@ CREATE DATABASE <replaceable class="parameter">name</replaceable>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">oid</replaceable></term>
<listitem>
<para>
The object identifier to be used for the new database. If this
parameter is not specified, the database will choose a suitable
OID automatically. This parameter is primarily intended for internal
use by <application>pg_upgrade</application>, and only
<application>pg_upgrade</application> can specify a value less
than 16384.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>