Hi, As we know, InnoDB has implicit primary key if a table hasn't defined a primary key. However MySQL server doesn't know this primary key, so this primary key will not apear in binlog. When we are using ROW format binlog for replication, if a table has no any indexes, that's a disaster. If a table without indexes do a DML (UPDATE/DELETE), of course it will run a long time in master, but in slave, it still need a long time. It will cause serious slave replication delay. For example: binlog_format=ROW; CREATE TABLE table1 ( col1 varchar(32), col2 int ); table1 hasn't any indexes, if table1 has 100 million rows, I do a query "UPDATE table1 SET col1='xxx' WHERE col2=100", and this query will effect 1 million rows. Then it has 1 million UPDATE events in binlog. After slave received these events, each events should scan all rows!!! It will cause serious replication delay! I saw:https://kb.askmonty.org/en/row-based-replication-with-no-primary-key/ But if no any indexes, it still a problem. I think mysql server can do the same thing as InnoDB do, if user doesn't define the primary key, mysql can add the primary key automatically. For example: If user create a table like "table1", we can do "ALTER TABLE table1 ADD __id bigint auto_increment, ADD PRIMARY KEY(__id)", so in fact, the "table1" structure is CREATE TABLE table1 ( col1 varchar(32), col2 int, __id bigint auto_increment primary key ); But when user do "SELECT * FROM table xxx" or "INSERT INTO table VALUES(xx)", we should ignore implicit primary key, "__id" will not apear in the result set. How do you think? Thanks, Lixun -- Senior Database Engineer @ Taobao.com Mobile Phone: +86 18658156856 (Hangzhou) Gtalk: penglixun(at)gmail.com Twitter: http://www.twitter.com/plinux Blog: http://www.penglixun.com