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Add GUC for temporarily disabling event triggers
In order to troubleshoot misbehaving or buggy event triggers, the documented advice is to enter single-user mode. In an attempt to reduce the number of situations where single-user mode is required (or even recommended) for non-extraordinary maintenance, this GUC allows to temporarily suspend event triggers. This was originally extracted from a larger patchset which aimed at supporting event triggers on login events. Reviewed-by: Ted Yu <[email protected]> Reviewed-by: Mikhail Gribkov <[email protected]> Reviewed-by: Justin Pryzby <[email protected]> Reviewed-by: Michael Paquier <[email protected] Reviewed-by: Robert Haas <[email protected]> Discussion: https://postgr.es/m/[email protected] Discussion: https://postgr.es/m/[email protected]
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‎doc/src/sgml/config.sgml‎

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@@ -9425,6 +9425,25 @@ SET XML OPTION { DOCUMENT | CONTENT };
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</listitem>
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</varlistentry>
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<varlistentry id="guc-event-triggers" xreflabel="event_triggers">
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<term><varname>event_triggers</varname> (<type>boolean</type>)
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<indexterm>
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<primary><varname>event_triggers</varname></primary>
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<secondary>configuration parameter</secondary>
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</indexterm>
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</term>
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<listitem>
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<para>
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Allow temporarily disabling execution of event triggers in order to
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troubleshoot and repair faulty event triggers. All event triggers will
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be disabled by setting it to <literal>false</literal>. Setting the value
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to <literal>true</literal> allows all event triggers to fire, this
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is the default value. Only superusers and users with the appropriate
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<literal>SET</literal> privilege can change this setting.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2 id="runtime-config-client-format">

‎doc/src/sgml/ref/create_event_trigger.sgml‎

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@@ -121,9 +121,12 @@ CREATE EVENT TRIGGER <replaceable class="parameter">name</replaceable>
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<para>
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Event triggers are disabled in single-user mode (see <xref
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linkend="app-postgres"/>). If an erroneous event trigger disables the
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database so much that you can't even drop the trigger, restart in
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single-user mode and you'll be able to do that.
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linkend="app-postgres"/>) as well as when
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<xref linkend="guc-event-triggers"/> is set to <literal>false</literal>.
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If an erroneous event trigger disables the database so much that you can't
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even drop the trigger, restart with <xref linkend="guc-event-triggers"/>
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set to <literal>false</literal> to temporarily disable event triggers, or
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in single-user mode, and you'll be able to do that.
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</para>
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</refsect1>
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‎src/backend/commands/event_trigger.c‎

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@@ -72,6 +72,9 @@ typedef struct EventTriggerQueryState
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static EventTriggerQueryState *currentEventTriggerState = NULL;
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/* GUC parameter */
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bool event_triggers = true;
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/* Support for dropped objects */
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typedef struct SQLDropObject
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{
@@ -657,8 +660,11 @@ EventTriggerDDLCommandStart(Node *parsetree)
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* wherein event triggers are disabled. (Or we could implement
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* heapscan-and-sort logic for that case, but having disaster recovery
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* scenarios depend on code that's otherwise untested isn't appetizing.)
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*
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* Additionally, event triggers can be disabled with a superuser-only GUC
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* to make fixing database easier as per 1 above.
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*/
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if (!IsUnderPostmaster)
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if (!IsUnderPostmaster || !event_triggers)
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return;
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runlist = EventTriggerCommonSetup(parsetree,
@@ -692,9 +698,9 @@ EventTriggerDDLCommandEnd(Node *parsetree)
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/*
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* See EventTriggerDDLCommandStart for a discussion about why event
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* triggers are disabled in single user mode.
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* triggers are disabled in single user mode or via GUC.
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*/
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if (!IsUnderPostmaster)
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if (!IsUnderPostmaster || !event_triggers)
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return;
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/*
@@ -740,9 +746,9 @@ EventTriggerSQLDrop(Node *parsetree)
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/*
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* See EventTriggerDDLCommandStart for a discussion about why event
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* triggers are disabled in single user mode.
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* triggers are disabled in single user mode or via a GUC.
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*/
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if (!IsUnderPostmaster)
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if (!IsUnderPostmaster || !event_triggers)
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return;
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/*
@@ -811,9 +817,9 @@ EventTriggerTableRewrite(Node *parsetree, Oid tableOid, int reason)
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/*
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* See EventTriggerDDLCommandStart for a discussion about why event
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* triggers are disabled in single user mode.
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* triggers are disabled in single user mode or via a GUC.
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*/
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if (!IsUnderPostmaster)
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if (!IsUnderPostmaster || !event_triggers)
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return;
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/*

‎src/backend/utils/misc/guc_tables.c‎

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@@ -37,6 +37,7 @@
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#include "catalog/namespace.h"
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#include "catalog/storage.h"
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#include "commands/async.h"
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#include "commands/event_trigger.h"
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#include "commands/tablespace.h"
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#include "commands/trigger.h"
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#include "commands/user.h"
@@ -2000,6 +2001,16 @@ struct config_bool ConfigureNamesBool[] =
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NULL, NULL, NULL
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},
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{
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{"event_triggers", PGC_SUSET, CLIENT_CONN_STATEMENT,
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gettext_noop("Enables event triggers."),
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gettext_noop("When enabled, event triggers will fire for all applicable statements."),
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},
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&event_triggers,
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true,
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NULL, NULL, NULL
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},
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/* End-of-list marker */
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{
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{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL

‎src/backend/utils/misc/postgresql.conf.sample‎

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@@ -706,6 +706,7 @@
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#xmloption = 'content'
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#gin_pending_list_limit = 4MB
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#createrole_self_grant = '' # set and/or inherit
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#event_triggers = on
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# - Locale and Formatting -
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‎src/include/commands/event_trigger.h‎

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@@ -29,6 +29,8 @@ typedef struct EventTriggerData
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CommandTag tag;
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} EventTriggerData;
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extern PGDLLIMPORT bool event_triggers;
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#define AT_REWRITE_ALTER_PERSISTENCE 0x01
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#define AT_REWRITE_DEFAULT_VAL 0x02
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#define AT_REWRITE_COLUMN_REWRITE 0x04

‎src/test/regress/expected/event_trigger.out‎

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@@ -616,3 +616,25 @@ SELECT
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DROP EVENT TRIGGER start_rls_command;
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DROP EVENT TRIGGER end_rls_command;
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DROP EVENT TRIGGER sql_drop_command;
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-- Check the GUC for disabling event triggers
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CREATE FUNCTION test_event_trigger_guc() RETURNS event_trigger
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LANGUAGE plpgsql AS $$
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DECLARE
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obj record;
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BEGIN
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FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
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LOOP
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RAISE NOTICE '% dropped %', tg_tag, obj.object_type;
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END LOOP;
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END;
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$$;
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CREATE EVENT TRIGGER test_event_trigger_guc
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ON sql_drop
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WHEN TAG IN ('DROP POLICY') EXECUTE FUNCTION test_event_trigger_guc();
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SET event_triggers = 'on';
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CREATE POLICY pguc ON event_trigger_test USING (FALSE);
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DROP POLICY pguc ON event_trigger_test;
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NOTICE: DROP POLICY dropped policy
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CREATE POLICY pguc ON event_trigger_test USING (FALSE);
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SET event_triggers = 'off';
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DROP POLICY pguc ON event_trigger_test;

‎src/test/regress/sql/event_trigger.sql‎

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@@ -471,3 +471,27 @@ SELECT
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DROP EVENT TRIGGER start_rls_command;
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DROP EVENT TRIGGER end_rls_command;
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DROP EVENT TRIGGER sql_drop_command;
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-- Check the GUC for disabling event triggers
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CREATE FUNCTION test_event_trigger_guc() RETURNS event_trigger
477+
LANGUAGE plpgsql AS $$
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DECLARE
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obj record;
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BEGIN
481+
FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
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LOOP
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RAISE NOTICE '% dropped %', tg_tag, obj.object_type;
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END LOOP;
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END;
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$$;
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CREATE EVENT TRIGGER test_event_trigger_guc
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ON sql_drop
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WHEN TAG IN ('DROP POLICY') EXECUTE FUNCTION test_event_trigger_guc();
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SET event_triggers = 'on';
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CREATE POLICY pguc ON event_trigger_test USING (FALSE);
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DROP POLICY pguc ON event_trigger_test;
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CREATE POLICY pguc ON event_trigger_test USING (FALSE);
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SET event_triggers = 'off';
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DROP POLICY pguc ON event_trigger_test;

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