Debezium series: source code reading snapshot reader

One 、Mysql Transaction isolation level

• Database transaction isolation level from low to high ：Read uncommitted、Read committed、Repeatable read and Serializable Four kinds of
• mysql Default transaction isolation level ：Repeatable read
• Repeatable read Repeated reading ： Avoid dirty reading 、 It can't be read repeatedly , But there may be unreal reading .
• When the transaction isolation level is repeatable , If the search condition has an index （ Include primary key index ） When , The default lock mode is next-key lock ; If the search criteria are not indexed , When updating data, the entire table will be locked . A gap is locked by a transaction , Other affairs cannot be done in this room