MySQL - Simple update is very slow and causing high load average with large amount of server Simple update is very slow  and causing high load average with large amount of server :

table name :

CREATE TABLE IF NOT EXISTS `LISTE_PROMOTION3` (
  `id_list_prom` int(11) NOT NULL AUTO_INCREMENT,
  `id_hotel` int(11) NOT NULL,
  `id_marche` int(11) NOT NULL,
  `lib_promo` varchar(250) NOT NULL,
  `etat_promo` enum('T','F') NOT NULL DEFAULT 'T',
  `type_promo` varchar(250) NOT NULL,
  `debut_vente` date NOT NULL,
  `fin_vente` date NOT NULL,
  `debut_sejour` date NOT NULL,
  `fin_sejour` date NOT NULL,
  `min_sty` int(11) NOT NULL,
  `max_sty` int(11) NOT NULL,
  `free_night` int(11) NOT NULL,
  `type_free_night` varchar(250) NOT NULL,
  `priorite_promo` int(11) NOT NULL,
  `typ_prom` varchar(250) NOT NULL,
  `pourcent_red_lpd` float NOT NULL,
  `pourcent_red_dp` float NOT NULL,
  `pourcent_red_dpplus` float NOT NULL,
  `pourcent_red_pc` float NOT NULL,
  `pourcent_red_pcplus` float NOT NULL,
  `pourcent_red_aisoft` float NOT NULL,
  `pourcent_red_allin` float NOT NULL,
  `pourcent_red_ultraai` float NOT NULL,
  `montant_red_lpd` float NOT NULL,
  `montant_red_dp` float NOT NULL,
  `montant_red_dpplus` float NOT NULL,
  `montant_red_pc` float NOT NULL,
  `montant_red_pcplus` float NOT NULL,
  `montant_red_aisoft` float NOT NULL,
  `montant_red_allin` float NOT NULL,
  `montant_red_ultraai` float NOT NULL,
  `id_agent` int(11) NOT NULL,
  `date_insertion` datetime NOT NULL,
  `date_modif` datetime NOT NULL,
  `id_agent_modif` int(11) NOT NULL,
  `typ_app_prom` varchar(250) NOT NULL,
  `sur_tarif` varchar(250) NOT NULL,
  `pourcent_red_ls` float NOT NULL,
  `montant_red_ls` float NOT NULL,
  PRIMARY KEY (`id_list_prom`),
  KEY `id_hotel` (`id_hotel`),
  KEY `etat_promo` (`etat_promo`),
  KEY `fin_vente` (`fin_vente`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=9480 ;


The table contains 9480 rows.

Query: 

UPDATE `LISTE_PROMOTION` SET `etat_promo` = 'T' WHERE `id_list_prom` = 9460;


This query update 1 row and takes around 25 seconds to complete and causing high load average with large amount of server.
Get rid of indexes on flags (etat_promo).  The Optimizer almost never uses such; it will prefer to do a table scan.  If you have some query that you think might be using that index, run the EXPLAIN and show us the query for further discussion.