Category Cache taking more time to excute

The below queries taking more time time execute in db i want to know to why these are executing.if these are executing also then taking more time.can we stop to execute these queries due to that my site is always going down on frequent basis.kindly provide anybody solution on priority basis.

Query_time: 30.124537

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Query_time: 6.132237

INSERT INTO cache_category (cid, data, created, expire, headers, serialized) VALUES ('n3590', 'a:1:{s:25:\"cat_node_get_cats3590:cid\";s:6:\"a:0:{}\";}', 1349934933, 0, '', 1);

Query_time: 10.392684

INSERT INTO cache_category (cid, data, created, expire, headers, serialized) VALUES ('n8331', 'a:1:{s:25:\"cat_node_get_cats8331:cid\";s:6:\"a:0:{}\";}', 1349935101, 0, '', 1);

Query_time: 11.199644
INSERT INTO cache_menu (cid, data, created, expire, headers, serialized) VALUES ('category-menu-trail-links:primary-links:all-cid:6336', 'category-menu-trail-links:primary-links:tree-data:e413fea325d97cafc31d1ce4f0c07910', 1349935101, 0, '', 0);