The transaction history log (THL) retains a copy of the SQL statements from each Primary host, and it is the information within the THL that is transferred between hosts and applied to the database. The THL information is written to disk and stored in the thl directory:

shell> ls -al /opt/continuent/thl/alpha/
total 2291984
drwxrwxr-x 2 tungsten tungsten      4096 Apr 16 13:44 .
drwxrwxr-x 3 tungsten tungsten      4096 Apr 15 15:53 ..
-rw-r--r-- 1 tungsten tungsten         0 Apr 15 15:53 disklog.lck
-rw-r--r-- 1 tungsten tungsten 100137585 Apr 15 18:13 thl.data.0000000001
-rw-r--r-- 1 tungsten tungsten 100134069 Apr 15 18:18 thl.data.0000000002
-rw-r--r-- 1 tungsten tungsten 100859685 Apr 15 18:26 thl.data.0000000003
-rw-r--r-- 1 tungsten tungsten 100515215 Apr 15 18:28 thl.data.0000000004
-rw-r--r-- 1 tungsten tungsten 100180770 Apr 15 18:31 thl.data.0000000005
-rw-r--r-- 1 tungsten tungsten 100453094 Apr 15 18:34 thl.data.0000000006
-rw-r--r-- 1 tungsten tungsten 100379260 Apr 15 18:35 thl.data.0000000007
-rw-r--r-- 1 tungsten tungsten 100294561 Apr 16 12:21 thl.data.0000000008
-rw-r--r-- 1 tungsten tungsten 100133258 Apr 16 12:24 thl.data.0000000009
-rw-r--r-- 1 tungsten tungsten 100293278 Apr 16 12:32 thl.data.0000000010
-rw-r--r-- 1 tungsten tungsten 100819317 Apr 16 12:34 thl.data.0000000011
-rw-r--r-- 1 tungsten tungsten 100250972 Apr 16 12:35 thl.data.0000000012
-rw-r--r-- 1 tungsten tungsten 100337285 Apr 16 12:37 thl.data.0000000013
-rw-r--r-- 1 tungsten tungsten 100535387 Apr 16 12:38 thl.data.0000000014
-rw-r--r-- 1 tungsten tungsten 100378358 Apr 16 12:40 thl.data.0000000015
-rw-r--r-- 1 tungsten tungsten 100198421 Apr 16 13:32 thl.data.0000000016
-rw-r--r-- 1 tungsten tungsten 100136955 Apr 16 13:34 thl.data.0000000017
-rw-r--r-- 1 tungsten tungsten 100490927 Apr 16 13:41 thl.data.0000000018
-rw-r--r-- 1 tungsten tungsten 100684346 Apr 16 13:41 thl.data.0000000019
-rw-r--r-- 1 tungsten tungsten 100225119 Apr 16 13:42 thl.data.0000000020
-rw-r--r-- 1 tungsten tungsten 100390819 Apr 16 13:43 thl.data.0000000021
-rw-r--r-- 1 tungsten tungsten 100418115 Apr 16 13:43 thl.data.0000000022
-rw-r--r-- 1 tungsten tungsten 100388812 Apr 16 13:44 thl.data.0000000023
-rw-r--r-- 1 tungsten tungsten  38275509 Apr 16 13:47 thl.data.0000000024

THL files are created on both the Primary and Replicas within the cluster. THL data can be examined using the thl command.

The THL is written into individual files, which are by default, no more than 1 GByte in size each. From the listing above, you can see that each file has a unique file index number. A new file is created when the file size limit is reached, and given the next THL log file number. To determine the sequence number that is stored within log, use the thl command:

shell> thl index
LogIndexEntry thl.data.0000000001(0:106)
LogIndexEntry thl.data.0000000002(107:203)
LogIndexEntry thl.data.0000000003(204:367)
LogIndexEntry thl.data.0000000004(368:464)
LogIndexEntry thl.data.0000000005(465:561)
LogIndexEntry thl.data.0000000006(562:658)
LogIndexEntry thl.data.0000000007(659:755)
LogIndexEntry thl.data.0000000008(756:1251)
LogIndexEntry thl.data.0000000009(1252:1348)
LogIndexEntry thl.data.0000000010(1349:1511)
LogIndexEntry thl.data.0000000011(1512:1609)
LogIndexEntry thl.data.0000000012(1610:1706)
LogIndexEntry thl.data.0000000013(1707:1803)
LogIndexEntry thl.data.0000000014(1804:1900)
LogIndexEntry thl.data.0000000015(1901:1997)
LogIndexEntry thl.data.0000000016(1998:2493)
LogIndexEntry thl.data.0000000017(2494:2590)
LogIndexEntry thl.data.0000000018(2591:2754)
LogIndexEntry thl.data.0000000019(2755:2851)
LogIndexEntry thl.data.0000000020(2852:2948)
LogIndexEntry thl.data.0000000021(2949:3045)
LogIndexEntry thl.data.0000000022(3046:3142)
LogIndexEntry thl.data.0000000023(3143:3239)
LogIndexEntry thl.data.0000000024(3240:3672)

The THL files are retained for seven days by default, although this parameter is configurable. Due to the nature and potential size required to store the information for the THL, you should monitor the disk space and usage.

The purge is continuous and is based on the date the log file was written. Each time the replicator finishes the current THL log file, it checks for files that have exceeded the defined retention configuration and spawns a job within the replicator to delete files older than the retention policy. Old files are only removed when the current THL log file rotates.

For working with THL files, the thl should be used. For further reading on the usage of this command and the various actions and tasks that can be performed, see the following sections: