Why MySQL query is too much slow with sending data status? I don't know why MySQL query is too slow with status "Sending data". I read many questions and found that this status comes when you have slow disk I/O. But I have a good server hosting with 500GB Hard disk and 8GB ram on my server. I am also using indexes on the required columns on each table. 

My query with left join:

Select  tbl_songs.id, tbl_songs.song_title, tbl_songs.picture,
        tbl_songs.description, tbl_songs.song_status, tbl_songs.latest,
        tbl_songs.popularity, tbl_songs.posted_date, tbl_songs.ranking_order,
        tbl_artists.id as artist_id
    from  tbl_songs
    left join  tbl_songs_artist  ON tbl_songs_artist.song_id=tbl_songs.id
    left join  tbl_artists  ON tbl_songs_artist.artist_id=tbl_artists.id
    where  MATCH (tbl_artists.artist_name)
           AGAINST ('Vectro Electro' IN BOOLEAN MODE)
    ORDER BY  tbl_songs.ids ASC
    limit  15


Here are few stats below on my server:

free -mh
             total       used       free     shared    buffers     cached
Mem:          7.8G       7.7G       123M        38M        88M       7.0G
-/+ buffers/cache:       617M       7.2G
Swap:         4.0G        33M       4.0G


top - 13:58:57 up 32 days,  9:43,  2 users,  load average: 2.07, 2.23, 1.76
Tasks: 133 total,   1 running, 132 sleeping,   0 stopped,   0 zombie
%Cpu(s): 10.6 us,  5.8 sy,  0.0 ni, 75.2 id,  8.4 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem:   8176780 total,  8038168 used,   138612 free,     1200 buffers
KiB Swap:  4194300 total,    40028 used,  4154272 free.  7424124 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 7683 mysql     20   0 1051368 186976   2984 S  65.8  2.3 161:18.73 mysqld
 4946 root      20   0  104564   3972   2884 S   0.7  0.0   0:00.08 sshd
   52 root      20   0       0      0      0 S   0.3  0.0  26:08.48 kswapd0


MySQL global variables are:

#tmpdir         = /tmp
tmpdir          = /var/mysqltmp

    max_heap_table_size = 512M
    tmp_table_size = 512M
    #sort_buffer_size = 218M
    #join_buffer_size = 5G
    #read_buffer_size = 5G
    #myisam_sort_buffer_size = 218M
    #innodb_buffer_pool_size=2G


    #
    #key_buffer             = 218M
    #max_allowed_packet     = 218M
    thread_stack            = 192K

# * Query Cache Configuration
#
query_cache_limit       = 1M
query_cache_size        = 0
query_cache_type = 0


[mysqldump]
quick
quote-names
#max_allowed_packet     = 218M

[isamchk]
#key_buffer             = 218M
Change LEFT JOIN to JOIN.

Change

AGAINST ('Vectro Electro' IN BOOLEAN MODE)


to

AGAINST ('+Vectro +Electro' IN BOOLEAN MODE)


Have this index on tbl_artists:  FULLTEXT(artist_name).

I assume that tbl_songs has PRIMARY KEY(id).

Assuming that tbl_songs_artist is a many-to-many mapping table, follow the tips in http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table

Is this a typo?  tbl_songs.ids

Use ENGINE=InnoDB.

Don't comment out the setting for innodb_buffer_pool_size.

Not more than 1% of RAM for these:

max_heap_table_size
tmp_table_size


("Sending status" is useless info.)