MYSQL data files are compressed to gz

I have drupal website, the database is about 10GB. I was checking the datadir of my drupal database and found that some files are .gz!! why is this? and does it affect performance?? the website is working fine and i can use those tables normally although there is no corresponding file for.gz (ie. I have content_type_company.MYD.gz in the data directory but there is no content_type_company.MYD)

the list is something like this:

ls -lhS *.gz
-rw-rw---- 1 mysql mysql 3.4M 2011-04-18 06:52 content_field_headline_image.MYI.gz
-rw-rw---- 1 mysql mysql 379K 2011-04-14 15:50 print_node_conf.MYD.gz
-rw-rw---- 1 mysql mysql 105K 2011-04-18 06:56 content_type_company.MYD.gz
-rw-rw---- 1 mysql mysql  22K 2011-04-14 15:50 nodewords.MYD.gz
-rw-rw---- 1 mysql mysql  18K 2011-04-18 06:59 content_field_company_fax.MYD.gz
-rw-rw---- 1 mysql mysql  18K 2011-04-18 06:59 content_field_company_email.MYI.gz
-rw-rw---- 1 mysql mysql 4.7K 2011-04-17 21:55 content_type_editor_choice.MYI.gz
-rw-rw---- 1 mysql mysql 4.2K 2011-02-01 09:15 content_node_field_instance.MYD.gz
-rw-rw---- 1 mysql mysql 2.7K 2011-01-31 14:03 content_node_field.MYD.gz
-rw-rw---- 1 mysql mysql 1.9K 2011-04-18 01:31 content_type_press_review.MYI.gz
-rw-rw---- 1 mysql mysql 1.4K 2011-04-18 06:59 users.MYI.gz
-rw-rw---- 1 mysql mysql 1.1K 2011-02-02 12:25 batch.MYD.gz
-rw-rw---- 1 mysql mysql 1.1K 2011-01-19 12:35 node_access.MYI.gz
-rw-rw---- 1 mysql mysql  801 2010-09-06 09:49 menu_custom.MYD.gz
-rw-rw---- 1 mysql mysql  679 2011-04-17 12:12 scheduler.MYI.gz
-rw-rw---- 1 mysql mysql  671 2011-01-12 11:24 users.frm.gz
-rw-rw---- 1 mysql mysql  659 2011-04-14 22:53 video_rendering.MYI.gz
-rw-rw---- 1 mysql mysql  570 2011-04-17 14:39 content_type_slideshow.MYD.gz
-rw-rw---- 1 mysql mysql  533 2011-02-02 09:46 permission.MYI.gz
-rw-rw---- 1 mysql mysql  471 2011-01-30 12:53 panels_display.MYD.gz
-rw-rw---- 1 mysql mysql  412 2010-09-07 14:41 content_field_slideshow_image.frm.gz
-rw-rw---- 1 mysql mysql  372 2011-01-12 11:24 date_formats.MYD.gz
-rw-rw---- 1 mysql mysql  355 2010-07-26 15:51 contact.frm.gz
-rw-rw---- 1 mysql mysql  351 2010-07-26 16:15 sessions.frm.gz
-rw-rw---- 1 mysql mysql  349 2011-03-28 18:02 cache_update.frm.gz
-rw-rw---- 1 mysql mysql  345 2011-03-28 18:03 ctools_object_cache.frm.gz
-rw-rw---- 1 mysql mysql  326 2010-07-26 15:54 print_mail_page_counter.frm.gz
-rw-rw---- 1 mysql mysql  317 2010-07-26 15:54 search_index.frm.gz
-rw-rw---- 1 mysql mysql  310 2010-07-26 15:51 i18n_strings.frm.gz
-rw-rw---- 1 mysql mysql  292 2010-07-26 15:49 authmap.frm.gz
-rw-rw---- 1 mysql mysql  291 2011-01-12 11:24 scheduler.frm.gz
-rw-rw---- 1 mysql mysql  286 2010-07-26 15:54 permission.frm.gz
-rw-rw---- 1 mysql mysql  275 2010-07-26 15:49 block_class.frm.gz
-rw-rw---- 1 mysql mysql  272 2010-07-26 15:51 captcha_points.frm.gz
-rw-rw---- 1 mysql mysql  269 2010-07-26 15:54 page_manager_weights.frm.gz
-rw-rw---- 1 mysql mysql  251 2011-03-28 18:03 imagecache_preset.frm.gz
-rw-rw---- 1 mysql mysql  249 2010-11-24 13:19 content_type_press_review.frm.gz
-rw-rw---- 1 mysql mysql  248 2011-01-26 09:21 aggregat开发者_运维技巧or_category_feed.frm.gz
-rw-rw---- 1 mysql mysql  243 2010-07-26 15:54 role.frm.gz
-rw-rw---- 1 mysql mysql  240 2010-07-26 16:15 variable.frm.gz
-rw-rw---- 1 mysql mysql  202 2010-08-09 13:20 stylizer.MYI.gz
-rw-rw---- 1 mysql mysql  192 2011-04-05 07:50 vocabulary_node_types.MYD.gz
-rw-rw---- 1 mysql mysql  152 2010-07-26 16:15 taxonomy_manager_merge.MYI.gz
-rw-rw---- 1 mysql mysql   78 2011-04-14 03:06 video_rendering.MYD.gz
-rw-rw---- 1 mysql mysql   58 2011-02-01 17:40 content_type_video_gallery.MYD.gz

The files are compressed to save space, of course, and gzip works like that - when a file called 'x' is gzipped, it's replaced by 'x.gz' the original file ''becomes'' the compressed file.

If the database works as expected, I wouldn't worry about it.

The size of gzipped files is much smaller than Your database size. Nothing to worry.