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Transaction Log
===============
Description
-----------
The Drizzle Transaction Log contains a sequence of
`Google Protocol Buffer <http://code.google.com/p/protobuf/>`_
messages that describe the transactions which have been run.
Configuration
-------------
Several server variables control the transaction log.
.. program:: drizzled
.. option:: --transaction-log.enable
Enable transaction log.
.. option:: --transaction-log.enable-checksum
Enable CRC32 Checksumming of each written transaction log entry
.. option:: --transaction-log.file=arg
Path to the file to use for transaction log. The default will be
:file:`transaction.log`.
.. option:: --transaction-log.use-replicator
Name of the replicator plugin to use (default='default_replicator')
.. option:: --transaction-log.flush-frequency=arg
* 0 : rely on operating system to sync log file (default)
* 1 : sync file at each transaction write
* 2 : sync log file once per second
.. option:: --transaction-log.num-write-buffers=arg
Number of slots for in-memory write buffers (default=8).
Transaction Log Messages
------------------------
Replication events are recorded using messages in the `Google Protocol Buffer
<http://code.google.com/p/protobuf/>`_ (GPB) format. See the :doc:`Replication
documentation </replication>` for more information.
Transaction Log Format
----------------------
Currently, the transaction log file uses a simple, single-file, append-only
format. The format of each entry in the transaction log file is::
4-bytes 4-bytes
+--------------+--------------+----------------------+
| Entry Type | Length | Serialized Message |
+--------------+--------------+----------------------+
The fields in the entry are:
* **Entry Type** - Type of message this entry contains. Currently,
this is always a Transaction GPB message.
* **Length** - The length, in bytes, of the serialized message.
* **Serialized Message** - The actual message data.
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