Data structure of MySQL transaction

Transaction is the core of the relational database, throughout the source code, first to look at the relevant data structure, uncover the veil:

The server layer and the InnoDB engine layer correspond to different data structures, but are related to each other:

1. The server tier requires the engine to register the transaction so that the server layer can reference it.
2. The INNODB layer needs to maintain the state of the transaction and the specific implementation of the state transition of the transaction.

1. Related Data structures

The following is a snapshot of the transaction interaction between server and InnoDB:

　　

Briefly describe:

The server layer associates all the participating engines through the stmt and all linked lists. Each connection, in the InnoDB engine assigns a TRX structure, which maintains to the end of the session.

No matter how many statements a transaction has, the number of participating table, an engine is registered only once, because a session currently has only one active transaction. The server notifies the engine to complete transaction-related operations by registering the engine.

Related Data structures:

Thd_trans
Ha_data
Ha_trx_info
Trx_sys_struct
Trx_struct

Specific reference to the source code.

2. How transactions Begin

Test: SELECT * FROM t

The engine of the T-table is InnoDB

1. First time connection

The first connection, when creating the ThD object, is the initial Ha_data[max_ha] array, but the initialization of the engine is completed.

The Thd->transaction.stmt/all are empty.

2. Create TRX: Corresponds to each connection, representing the transaction context of the connection

When the statement executes, create the INNODB TRX structure, corresponding to the ha_data[8].ha_ptr.

function Call Stack:

Ha_innobase::store_lock

Check_trx_exists
Innobase_trx_allocate
Trx_allocate_for_mysql:
1. Trx_create: Creating a TRX Structure
2. Incrementing the Trx_n_mysql_transactions global count
3. Join the Global link list trx_sys->mysql_trx_list
Innobase_trx_init

Initialize TRX associated with current server layer THD

Note: During the execution of the statement, all table of the polling statement is assigned TRX in the Get_table_lock process because the transaction and the lock are related. All transaction-related registrations are closely tied to the table_lock process.

3. Register the engine that participates in the transaction to Thd->transaction

Ha_info->is_started () If Ha_info is already associated with the engine, then the transaction has already started and has been registered.

Here are two things to do:

1. If autocommit=0

InnoDB engine needs to register Stmt,all two linked list

2. If autocommit=1

The InnoDB engine only needs to register the stmt linked list

The results after registration are:

(GDB) P Thd->transaction.all.ha_list.m_ht.db_type
$66 = Db_type_innodb

4. Transaction Submission

If autocommit=0, when the transaction commits:

Release Lock:

Ha_innobase::external_lock

trx->n_mysql_tables_in_use--; Clean the TRX structure during the release of table lock

Submit:

Trans_commit_stmt
if (thd->transaction.stmt.ha_list)
Ha_commit_trans (THD, FALSE);

Thd->transaction.stmt.reset (); Reset stmt Linked List
Commit_one_phase_low; resets ha_trx_info to no use status.

Here is just the beginning of the business, not to be continued ...