Documentation for Confluence 2.5.4 - 2.5.8.
Documentation for [Confluence Cloud] and the latest Confluence Server is available too. 
To support the Unicode character set, create your database like this:
For 8.2.2 or later:
db2 create database <name> using codeset utf-8 territory us pagesize 8 k
Before 8.2.2
db2 create database <name> using codeset utf-8 territory us
db2 drop tablespace userspace1
db2 create bufferpool bufpool8k <number of pages> pagesize 8 k
db2 create tablespace userspace1 pagesize 8 k managed by database using \(file \'<location>\'
<number of pages>\) bufferpool bufpool8k
The territory may not be important when using UTF-8, but it must be included.
"With their potentially large size, LOBs can slow down the performance of your database system significantly when moved into or out of a database. Even though DB2 does not allow logging of a LOB value greater than 1 GB, LOB values with sizes approaching 1 GB can quickly push the database log to near capacity. An error, SQLCODE -355 (SQLSTATE 42993), results from attempting to log a LOB greater than 1 GB in size. The lob-options-clause in the CREATE TABLE and ALTER TABLE statements allows users to turn off logging for a particular LOB column. Although setting the option to NOT LOGGED will improve performance, changes to the LOB values after the most recent backup are lost during roll-forward recovery."
Although one could set the length for the CustomClobType in BodyContent.hbm.xml field length to larger sizes, say 2^31 to allow storing of BLOBs up to the size of 2 Gb, DB2 maximum length can only be set to 2^30, 1GB.
<property name="body" type="com.atlassian.confluence.core.persistence.hibernate.CustomClobType" update="true" insert="true"
column="BODY" length="1073741824" />
Refer to Configuring Database Character Encoding.
If you are using DB2, and are upgrading Confluence from version 2.2 or older, the 'hibernate.dialect' property in the confluence.cfg.xml file needs to be changed to 'com.atlassian.hibernate.dialect.DB2Dialect' like so:
<property name="hibernate.dialect">com.atlassian.hibernate.dialect.DB2Dialect</property>
At the time of writing this, there is an open bug with the encoding test when using DB2. Details are here: CONF-8588.
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