Shulou(Shulou.com)06/01 Report--

one。 Data rows hidden columns

Innodb implements three hidden fields for each row of records

6-byte transaction ID (DB_TRX_ID)

7-byte rollback pointer (DB_ROLL_PTR)

Hidden ID

Transaction 1 modifies the row value process:

X Lock Lock the row-> record redo log-> copy the pre-modified value of the row to undo-> modify the value of the current row, fill in the transaction number, and point the rollback pointer to the pre-modified row in undo log

Transaction 2 modifies the row value process:

As with transaction 1, there are two rows of records in undo log, which are connected by a rollback pointer

II. The process of applying MVCC to RC and RR

RC transaction starts (1). Before executing the SQL statement, output the inactive transaction information in the system to a copy, TRX _ list (2). The user starts to read records at the current SQL, assuming that the read record transaction ID is trx_id_0 (3). Find out the earliest transaction trx_id_1 and the latest transaction trx_id_2 (4) in trx_list. If trx_id_0

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