Joomla MySQL 性能

My problem is about MySQL query performance. Database includes about 60000 rows in content table, and the query seen below (core com_content articles model query) execution time is about 6 seconds.Very slow.

SELECT a.id,
   a.title,
   a.alias,
   a.title_alias,
   a.introtext,
   a.checked_out,
   a.checked_out_time,
   a.catid,
   a.created,
   a.created_by,
   a.created_by_alias,
   CASE
     WHEN a.modified = 0 THEN a.created
     ELSE a.modified
   END as modified,
   a.modified_by,
   uam.name as modified_by_name,
   CASE
     WHEN a.publish_up = 0 THEN a.created
     ELSE a.publish_up
   END as publish_up,
   a.publish_down,
   a.images,
   a.urls,
   a.attribs,
   a.metadata,
   a.metakey,
   a.metadesc,
   a.access,
   a.hits,
   a.xreference,
   a.featured,
   LENGTH(a.fulltext) AS readmore,
   CASE
     WHEN badcats.id is not null THEN 0
     ELSE a.state
   END AS state,
   c.title AS category_title,
   c.path AS category_route,
   c.access AS category_access,
   c.alias AS category_alias,
   CASE
     WHEN a.created_by_alias > ' ' THEN a.created_by_alias
     ELSE ua.name
   END AS author,
   ua.email AS author_email,
   contact.id as contactid,
   parent.title as parent_title,
   parent.id as parent_id,
   parent.path as parent_route,
   parent.alias as parent_alias,
   ROUND(v.rating_sum / v.rating_count, 0) AS rating,
   v.rating_count as rating_count,
   c.published,
   CASE
     WHEN badcats.id is null THEN c.published
     ELSE 0
   END AS parents_published
  FROM #__content AS a
 LEFT JOIN #__content_frontpage AS fp ON fp.content_id = a.id
 LEFT JOIN #__categories AS c ON c.id = a.catid
 LEFT JOIN #__users AS ua ON ua.id = a.created_by
 LEFT JOIN #__users AS uam ON uam.id = a.modified_by
 LEFT JOIN 
 (SELECT contact.user_id, MAX(contact.id) AS id, contact.language FROM
  #__contact_details AS contact WHERE contact.published = 1 GROUP BY
   contact.user_id, contact.language) AS contact ON contact.user_id =
    a.created_by
 LEFT JOIN #__categories as parent ON parent.id = c.parent_id
 LEFT JOIN #__content_rating AS v ON a.id = v.content_id
 LEFT OUTER JOIN 
 (SELECT cat.id as id FROM #__categories AS cat JOIN #__categories AS
  parent ON cat.lft BETWEEN parent.lft AND parent.rgt WHERE parent.extension
   = 'com_content' AND parent.published != 1 GROUP BY cat.id) AS badcats ON
    badcats.id = c.id
  WHERE CASE
  WHEN badcats.id is null THEN a.state
  ELSE 0
 END = 1 AND
  a.featured = 0 AND
  a.id NOT IN (8921, 33722, 33728, 33729, 34187, 35047, 36784, 36236, 33724,
   19522) AND
  a.catid IN (8, 39, 40, 38, 72, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
   20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 36, 37, 41) AND
  (a.publish_up = '0000-00-00 00:00:00' OR
  a.publish_up <= '2013-06-12 06:44:44') AND
  (a.publish_down = '0000-00-00 00:00:00' OR
  a.publish_down >= '2013-06-12 06:44:44')
    GROUP BY a.id,
     a.title,
     a.alias,
     a.title_alias,
     a.introtext,
     a.checked_out,
     a.checked_out_time,
     a.catid,
     a.created,
     a.created_by,
     a.created_by_alias,
     a.created,
     a.modified,
     a.modified_by,
     uam.name,
     a.publish_up,
     a.attribs,
     a.metadata,
     a.metakey,
     a.metadesc,
     a.access,
     a.hits,
     a.xreference,
     a.featured,
     a.fulltext,
     a.state,
     a.publish_down,
     badcats.id,
     c.title,
     c.path,
     c.access,
     c.alias,
     uam.id,
     ua.name,
     ua.email,
     contact.id,
     parent.title,
     parent.id,
     parent.path,
     parent.alias,
     v.rating_sum,
     v.rating_count,
     c.published,
     c.lft,
     a.ordering,
     parent.lft,
     fp.ordering,
     c.id,
     a.images,
     a.urls
 ORDER BY publish_up DESC
 LIMIT 4,  4

例如当我改变时

 (a.publish_up = '0000-00-00 00:00:00' OR
  a.publish_up <= '2013-06-12 06:44:44') AND
  (a.publish_down = '0000-00-00 00:00:00' OR
  a.publish_down >= '2013-06-12 06:44:44')

与

(a.publish_up >= DATE_SUB(NOW(), INTERVAL 2 MONTH))

查询执行时间约为 0.5 秒

skip-external-locking
skip-name-resolve
key_buffer_size = 128M
max_connections=1024
max_allowed_packet = 16M
net_buffer_length = 8K
table_open_cache = 512
table_cache = 2048
join_buffer_size = 128M
read_buffer_size = 128M
sort_buffer_size = 128M
read_rnd_buffer_size=2M
myisam_sort_buffer_size=128M
thread_concurrency=16
query_cache_size = 128M  
query_cache_type=1
thread_cache_size = 1300
query_cache_limit=128M
max_heap_table_size = 1024M
tmp_table_size = 1024M