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Repair pg_upgrade for identity sequences with non-default persistence.

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Since we introduced unlogged sequences in v15, identity sequences
have defaulted to having the same persistence as their owning table.
However, it is possible to change that with ALTER SEQUENCE, and
pg_dump tries to preserve the logged-ness of sequences when it doesn't
match (as indeed it wouldn't for an unlogged table from before v15).

The fly in the ointment is that ALTER SEQUENCE SET [UN]LOGGED fails
in binary-upgrade mode, because it needs to assign a new relfilenode
which we cannot permit in that mode.  Thus, trying to pg_upgrade a
database containing a mismatching identity sequence failed.

To fix, add syntax to ADD/ALTER COLUMN GENERATED AS IDENTITY to allow
the sequence's persistence to be set correctly at creation, and use
that instead of ALTER SEQUENCE SET [UN]LOGGED in pg_dump.  (I tried to
make SET [UN]LOGGED work without any pg_dump modifications, but that
seems too fragile to be a desirable answer.  This way should be
markedly faster anyhow.)

In passing, document the previously-undocumented SEQUENCE NAME option
that pg_dump also relies on for identity sequences; I see no value
in trying to pretend it doesn't exist.

Per bug #18618 from Anthony Hsu.
Back-patch to v15 where we invented this stuff.

Discussion: https://postgr.es/m/18618-d4eb26d669ed110a@postgresql.org
This commit is contained in:
Tom Lane
2024-09-17 15:53:26 -04:00
parent 2520226c95
commit 918e21d251
7 changed files with 112 additions and 41 deletions
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17
doc/src/sgml/ref/create_table.sgml
View File

@ -924,8 +924,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
<para>
This clause creates the column as an <firstterm>identity
column</firstterm>. It will have an implicit sequence attached to it
and the column in new rows will automatically have values from the
sequence assigned to it.
and in newly-inserted rows the column will automatically have values
from the sequence assigned to it.
Such a column is implicitly <literal>NOT NULL</literal>.
</para>
@ -955,9 +955,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</para>
<para>
The optional <replaceable>sequence_options</replaceable> clause can be
used to override the options of the sequence.
See <xref linkend="sql-createsequence"/> for details.
The optional <replaceable>sequence_options</replaceable> clause can
be used to override the parameters of the sequence. The available
options include those shown for <xref linkend="sql-createsequence"/>,
plus <literal>SEQUENCE NAME <replaceable>name</replaceable></literal>,
<literal>LOGGED</literal>, and <literal>UNLOGGED</literal>, which
allow selection of the name and persistence level of the
sequence. Without <literal>SEQUENCE NAME</literal>, the system
chooses an unused name for the sequence.
Without <literal>LOGGED</literal> or <literal>UNLOGGED</literal>,
the sequence will have the same persistence level as the table.
</para>
</listitem>
</varlistentry>