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Commita063d84

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doc: Expand documentation of session_replication_role
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‎doc/src/sgml/config.sgml

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@@ -6506,8 +6506,30 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
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superuser privilege and results in discarding any previously cached
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query plans. Possible values are <literal>origin</literal> (the default),
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<literal>replica</literal> and <literal>local</literal>.
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See <xref linkend="sql-altertable"/> for
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more information.
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</para>
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<para>
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The intended use of this setting is that logical replication systems
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set it to <literal>replica</literal> when they are applying replicated
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changes. The effect of that will be that triggers and rules (that
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have not been altered from their default configuration) will not fire
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on the replica. See the <xref linkend="sql-altertable"/> clauses
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<literal>ENABLE TRIGGER</literal> and <literal>ENABLE RULE</literal>
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for more information.
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</para>
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<para>
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PostgreSQL treats the settings <literal>origin</literal> and
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<literal>local</literal> the same internally. Third-party replication
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systems may use these two values for their internal purposes, for
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example using <literal>local</literal> to designate a session whose
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changes should not be replicated.
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</para>
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<para>
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Since foreign keys are implemented as triggers, setting this parameter
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to <literal>replica</literal> also disables all foreign key checks,
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which can leave data in an inconsistent state if improperly used.
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</para>
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</listitem>
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</varlistentry>

‎doc/src/sgml/ref/alter_table.sgml

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@@ -456,14 +456,30 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
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requires superuser privileges; it should be done with caution since
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of course the integrity of the constraint cannot be guaranteed if the
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triggers are not executed.
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</para>
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<para>
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The trigger firing mechanism is also affected by the configuration
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variable <xref linkend="guc-session-replication-role"/>. Simply enabled
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triggers will fire when the replication role is <quote>origin</quote>
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triggers(the default)will fire when the replication role is <quote>origin</quote>
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(the default) or <quote>local</quote>. Triggers configured as <literal>ENABLE
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REPLICA</literal> will only fire if the session is in <quote>replica</quote>
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mode, and triggers configured as <literal>ENABLE ALWAYS</literal> will
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fire regardless of the current replication mode.
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fire regardless of the current replication role.
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</para>
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<para>
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The effect of this mechanism is that in the default configuration,
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triggers do not fire on replicas. This is useful because if a trigger
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is used on the origin to propagate data between tables, then the
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replication system will also replicate the propagated data, and the
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trigger should not fire a second time on the replica, because that would
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lead to duplication. However, if a trigger is used for another purpose
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such as creating external alerts, then it might be appropriate to set it
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to <literal>ENABLE ALWAYS</literal> so that it is also fired on
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replicas.
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</para>
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<para>
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This command acquires a <literal>SHARE ROW EXCLUSIVE</literal> lock.
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</para>
@@ -481,6 +497,12 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
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are always applied in order to keep views working even if the current
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session is in a non-default replication role.
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</para>
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<para>
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The rule firing mechanism is also affected by the configuration variable
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<xref linkend="guc-session-replication-role"/>, analogous to triggers as
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described above.
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</para>
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</listitem>
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</varlistentry>
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