performance - Slow MySQL Updates/Inserts/Deletes -

i seem having slow inserts, updates , deletes on tables on specific database mysql. not lot of data in tables (from 2k 20k). small number of columns (5-10), indexes (two of them), , no duplicate index issue. i'm running mysql 5.0.45 myisam.

i run following query , takes 5-7 seconds:

update accounts set updated_at = '2010-10-09 11:22:53' id = 8; 

selects seem come right away.

explain gives me following:

+----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+ | id | select_type | table    | type  | possible_keys | key     | key_len | ref  | rows |       | +----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+ |  1 | simple      | accounts | index | null          | primary | 4       | null | 1841 | using index |  +----+-------------+----------+-------+---------------+---------+---------+------+------+-------------+ 

the profiler doesn't show significant data other seemingly high number of context switches:

+----------------------+----------+-------------------+---------------------+ | status               | duration | context_voluntary | context_involuntary | +----------------------+----------+-------------------+---------------------+ | (initialization)     | 0.000057 |                 0 |                   0 |  | checking permissions | 0.000008 |                 0 |                   0 |  | opening tables       | 0.000013 |                 0 |                   0 |  | system lock          | 0.000005 |                 0 |                   0 |  | table lock           | 0.000005 |                 0 |                   0 |  | init                 | 0.000061 |                 0 |                   0 |  | updating             | 0.000101 |                 0 |                   0 |  | end                  | 7.957233 |              7951 |                   2 |  | query end            | 0.000008 |                 0 |                   0 |  | freeing items        | 0.000011 |                 0 |                   0 |  | closing tables       | 0.000007 |                 1 |                   0 |  | logging slow query   | 0.000002 |                 0 |                   0 |  +----------------------+----------+-------------------+---------------------+ 

this might help:

+----------------------+----------+-----------------------+---------------+-------------+ | status               | duration | source_function       | source_file   | source_line | +----------------------+----------+-----------------------+---------------+-------------+ | (initialization)     | 0.000057 | check_access          | sql_parse.cc  |        5306 |  | checking permissions | 0.000008 | open_tables           | sql_base.cc   |        2629 |  | opening tables       | 0.000013 | mysql_lock_tables     | lock.cc       |         153 |  | system lock          | 0.000005 | mysql_lock_tables     | lock.cc       |         162 |  | table lock           | 0.000005 | mysql_update          | sql_update.cc |         167 |  | init                 | 0.000061 | mysql_update          | sql_update.cc |         429 |  | updating             | 0.000101 | mysql_update          | sql_update.cc |         560 |  | end                  | 7.957233 | mysql_execute_command | sql_parse.cc  |        5122 |  | query end            | 0.000008 | mysql_parse           | sql_parse.cc  |        6116 |  | freeing items        | 0.000011 | dispatch_command      | sql_parse.cc  |        2146 |  | closing tables       | 0.000007 | log_slow_statement    | sql_parse.cc  |        2204 |  | logging slow query   | 0.000002 | dispatch_command      | sql_parse.cc  |        2169 |  +----------------------+----------+-----------------------+---------------+-------------+ 

additional info: it's running on centos-5 vps 4 gigs of ram guaranteed. no index on updated_at column , not triggers anywhere.

[new things tried]

1. created new table (using like) running innodb , inserted records 1 of affected tables. (same problem)
2. backed database , restored different database within same server instance. (same problem)
3. restored same backup local machine , didn't have problem.
4. tried database within same mysql server instance has problem database , other database (a wordpress db) ran updates/inserts/deletes fine.
5. restarted mysqld , restarted entire server last night (same problem)
6. updated mysql version 5.0.77 (same problem)
7. deleted indexes 1 of affected tables (same problem)

any ideas @ next or might issue? seems more of recent problem though can't when started show exactly.

if have variable length rows, might need run optimize table occasionally.