Slow amount (*) on innoDB

Question

I have a table message_messagewith 3,000,000 records.

when I make a request to count (*), it is very slow ...:

mysql> select count(*) from message_message;

+ ---------- +

| count (*) |

+ ---------- +

| 2819416 |

+ ---------- +

1 line in a set (2 min. 35.35 sec.)

explain it: mysql> explain select count(*) from message_message;

| id | SELECT_TYPE | table | type | possible_keys | key | key_len | ref | strings | Extra |

| 1 | SIMPLE | message_message | index | NULL | PRIMARY | 4 | NULL | 2939870 | Using the index |

1 row in a set (0.02 sec)

what will happen

Answer 1

This Post InnoDB , , MyISAM, .

where, , , InnoDB , MyISAM, , .

Answer 2

, num_rows . Count(...) , ( GROUP BY).