Transaction logs

This topic describes different types of transaction logs.

Transaction types

Based on the transaction operation type and the distribution of accessed data, transactions can be divided into two types:

• Local transaction: The information about a local transaction is maintained on the same OBServer node as the one that stores data accessed by the transaction. Such a transaction accesses only data in the same partition.
• Distributed transaction: The information about a distributed transaction is maintained on a different node from the one that stores data accessed by the transaction. Such a transaction accesses data in multiple partitions.

Transaction log types

Based on the generation stage of transaction logs, transaction logs can be divided into two types:

• Transaction execution logs
• Transaction commit logs

Transaction execution logs

If the transaction modifications must be persisted when a transaction is executed, a log is generated to persist the modifications of this transaction. Logs of this type are referred to as transaction execution logs. The following table describes different types of transaction execution logs.

Transaction commit logs

After a transaction enters the commit stage, the transaction modifications must be persisted. In this stage, different types of transaction logs are generated based on the transaction type.

• The following table describes the types of logs generated when a distributed transaction is committed.

  Log type	Internal type value	Description
  OB_LOG_TRANS_REDO	0x1	The redo log of the distributed transaction, which contains the transaction modifications.
  OB_LOG_TRANS_PREPARE	0x2	The prepare log of the distributed transaction.
  OB_LOG_TRANS_REDO_WITH_PREPARE	0x3	The prepare log that contains the transaction modifications (redo log) of the distributed transaction.
  OB_LOG_TRANS_COMMIT	0x4	The commit log of the distributed transaction, which indicates that the transaction has been committed.
  OB_LOG_TRANS_ABORT	0x8	The abort log of the distributed transaction, which indicates that the transaction has been rolled back.
  OB_LOG_TRANS_CLEAR	0x10	The clear log of the distributed transaction, which is used to release transaction context information.

• The following table describes the types of logs generated when a local transaction is committed.

  Log type	Internal type value	Description
  OB_LOG_SP_TRANS_REDO	0x20	The redo log of the local transaction, which contains the transaction modifications.
  OB_LOG_SP_TRANS_COMMIT	0x40	The commit log of the local transaction, which indicates that the transaction has been committed. It contains the transaction modifications (redo log).
  OB_LOG_SP_TRANS_ABORT	0x80	The abort log of the local transaction, which indicates that the transaction has been rolled back.

Transaction ID

Transactions on an OBServer node are uniquely identified by transaction IDs. Therefore, transaction IDs must be unique on the same OBServer node. The following example shows the structure of a unique transaction ID:

class ObTransID
{
  uint64_t hv_;
  common::ObAddr server_;
  int64_t inc_;
  int64_t timestamp_;
}

The following table describes the fields.