Function EventTriggerBeginCompleteQuery

src/backend/commands/event_trigger.c:1106–1137

* Prepare event trigger state for a new complete query to run, if necessary; * returns whether this was done. If it was, EventTriggerEndCompleteQuery must * be called when the query is done, regardless of whether it succeeds or fails * -- so use of a PG_TRY block is mandatory. */

 * -- so use of a PG_TRY block is mandatory.
 */
bool
EventTriggerBeginCompleteQuery(void)
{
	EventTriggerQueryState *state;
	MemoryContext cxt;

	/*
	 * Currently, sql_drop, table_rewrite, ddl_command_end events are the only
	 * reason to have event trigger state at all; so if there are none, don't
	 * install one.
	 */
	if (!trackDroppedObjectsNeeded())
		return false;

	cxt = AllocSetContextCreate(TopMemoryContext,
								"event trigger state",
								ALLOCSET_DEFAULT_SIZES);
	state = MemoryContextAlloc(cxt, sizeof(EventTriggerQueryState));
	state->cxt = cxt;
	slist_init(&(state->SQLDropList));
	state->in_sql_drop = false;
	state->table_rewrite_oid = InvalidOid;

	state->commandCollectionInhibited = currentEventTriggerState ?
		currentEventTriggerState->commandCollectionInhibited : false;
	state->currentCommand = NULL;
	state->commandList = NIL;
	state->previous = currentEventTriggerState;
	currentEventTriggerState = state;

	return true;
}

/*
 * Query completed (or errored out) -- clean up local state, return to previous