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Disable event triggers in standalone mode.

Per discussion, this seems necessary to allow recovery from broken eventtriggers, or broken indexes on pg_event_trigger.Dimitri Fontaine

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Lines changed: 9 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -108,15 +108,22 @@ CREATE EVENT TRIGGER <replaceable class="PARAMETER">name</replaceable>`
`108`	`108`	`<title>Notes</title>`
`109`	`109`
`110`	`110`	`<para>`
`111`		`- To create a trigger on a event, the user must be superuser.`
	`111`	`+ Only superusers can create event triggers.`
	`112`	`+ </para>`
	`113`	`+`
	`114`	`+ <para>`
	`115`	`+ Event triggers are disabled in single-user mode (see <xref`
	`116`	`+ linkend="app-postgres">). If an erroneous event trigger disables the`
	`117`	`+ database so much that you can't even drop the trigger, restart in`
	`118`	`+ single-user mode and you'll be able to do that.`
`112`	`119`	`</para>`
`113`	`120`	`</refsect1>`
`114`	`121`
`115`	`122`	`<refsect1 id="sql-createeventtrigger-examples">`
`116`	`123`	`<title>Examples</title>`
`117`	`124`
`118`	`125`	`<para>`
`119`		`- Forbid the execution of any <link linkend="ddl">ddl</link> command:`
	`126`	`+ Forbid the execution of any <link linkend="ddl">DDL</link> command:`
`120`	`127`
`121`	`128`	`<programlisting>`
`122`	`129`	`CREATE OR REPLACE FUNCTION abort_any_command()`

Lines changed: 19 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -566,6 +566,25 @@ EventTriggerDDLCommandStart(Node *parsetree)`
`566`	`566`	`constchar*tag;`
`567`	`567`	`EventTriggerDatatrigdata;`
`568`	`568`
	`569`	`+/*`
	`570`	`+ * Event Triggers are completely disabled in standalone mode. There are`
	`571`	`+ * (at least) two reasons for this:`
	`572`	`+ *`
	`573`	`+ * 1. A sufficiently broken event trigger might not only render the`
	`574`	`+ * database unusable, but prevent disabling itself to fix the situation.`
	`575`	`+ * In this scenario, restarting in standalone mode provides an escape`
	`576`	`+ * hatch.`
	`577`	`+ *`
	`578`	`+ * 2. BuildEventTriggerCache relies on systable_beginscan_ordered, and`
	`579`	`+ * therefore will malfunction if pg_event_trigger's indexes are damaged.`
	`580`	`+ * To allow recovery from a damaged index, we need some operating mode`
	`581`	`+ * wherein event triggers are disabled. (Or we could implement`
	`582`	`+ * heapscan-and-sort logic for that case, but having disaster recovery`
	`583`	`+ * scenarios depend on code that's otherwise untested isn't appetizing.)`
	`584`	`+ */`
	`585`	`+if (!IsUnderPostmaster)`
	`586`	`+return;`
	`587`	`+`
`569`	`588`	`/*`
`570`	`589`	`* We want the list of command tags for which this procedure is actually`
`571`	`590`	`* invoked to match up exactly with the list that CREATE EVENT TRIGGER`

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