performance tuning on simple update query


here is the simple update query which takes more than 20sec :roll:

UPDATE audience_member_reg SET completed_page_no = 2, reg_datetime = ‘2009-03-28 07:13:45’ WHERE audience_member_reg_id = 6640737;

explain statements are,

mysql> explain select completed_page_no,reg_datetime from audience_member_reg where audience_member_reg_id = 6640737\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: NULL
type: NULL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: NULL
Extra: Impossible WHERE noticed after reading const tables
1 row in set (0.00 sec)

is there anyway this query can be improved upon? could anyone please help me out. thanks for your response.

Use explain with valid audience_member_reg_id.

What is the type of the table: myisam or innodb ?
How many rows are there ?

Thanks for you reply.

this is Innodb engine. this table has nearly 5 millon of records.

and audience_member_reg_id is the primary key.