select count(*),tablename,field from housekeeper group by tablename, field order by 1 desc; 
count   tablename   field
5618227 trends_uint itemid
5618227 history_text    itemid
5618227 history_uint    itemid
5618227 trends  itemid
5618227 history itemid
5618227 history_log itemid
5618227 history_str itemid
56  events  lldruleid
56  events  itemid
2   events  triggerid

...
static unsigned char poption_mode_regular 	= ZBX_HK_MODE_REGULAR;
static unsigned char poption_global_disabled	= ZBX_HK_OPTION_DISABLED;
...
/* Housekeeper table mapping to housekeeping configuration values.    */
/* This mapping is used to exclude disabled tables from housekeeping  */
/* cleanup procedure.                                                 */
static zbx_hk_cleanup_table_t	hk_cleanup_tables[] = {
	{"history",		&cfg.hk.history_mode,	&cfg.hk.history_global},
	{"history_log",		&cfg.hk.history_mode,	&cfg.hk.history_global},
	{"history_str",		&cfg.hk.history_mode,	&cfg.hk.history_global},
	{"history_text",	&cfg.hk.history_mode,	&cfg.hk.history_global},
	{"history_uint",	&cfg.hk.history_mode,	&cfg.hk.history_global},
	{"trends",		&cfg.hk.trends_mode,	&cfg.hk.trends_global},
	{"trends_uint",		&cfg.hk.trends_mode,	&cfg.hk.trends_global},
	/* force events housekeeping mode on to perform problem cleanup when events housekeeping is disabled */
	{"events",		&poption_mode_regular,	&poption_global_disabled},
	{NULL}
};
...
/* assemble list of tables included in the housekeeping procedure */
	for (table = hk_cleanup_tables; NULL != table->name; table++)
	{
		if (ZBX_HK_MODE_REGULAR != *table->poption_mode)
			continue;

		table_name_esc = DBdyn_escape_string(table->name);

		zbx_chrcpy_alloc(&sql, &sql_alloc, &sql_offset, '\'');
		zbx_strcpy_alloc(&sql, &sql_alloc, &sql_offset, table_name_esc);
		zbx_strcpy_alloc(&sql, &sql_alloc, &sql_offset, "',");

		zbx_free(table_name_esc);
	}
...