History: InnoDB

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            ! About InnoDB
Support for InnoDB was introduced in Tiki 8. InnoDB is the default engine since Tiki 18.

InnoDB provides several benefits over the MyISAM engine. It is crash-proof (the database will automatically recover errors upon restart).

Additionally, InnoDB supports (multi-statement) transactions and row-level locking, i.e. updates, inserts and deletes will no longer lock the whole file/table. It also supports referential integrity by the use of foreign keys. But these features are currently not used by vanilla Tiki. Customized Tiki versions could take advantage of these features, e.g. if the tiki_pages table is linked from a custom table.

The source code lives here: https://gitlab.com/tikiwiki/tiki/-/blob/master/db/tiki_convert_myisam_to_innodb.sql

! Installing with InnoDB
When creating the Tiki database, the user can choose to use MyISAM or InnoDB. Once the choice is made, Tiki will remember the selection.

! Migrating existing MyISAM databases
Migration steps:
# Make sure InnoDB is integrated in the standard/Git Tiki release. Otherwise you may be unable to do any upgrades later.
# Do a full backup of your current database/installation
# InnoDB does not support fulltext search in MySQL versions prior to 5.6 and in MariaDB 5. If you use one of these:
## Disable fulltext search in Tiki, since you won't be able to disable it from the GUI after the conversion.
## Drop all MyISAM fulltext indexes
# Alter the database engine for all tables to InnoDB

Steps 3.2 and 4 are defined in the file db/tiki_convert_myisam_to_innodb.sql. This script is fragile and may not treat all tables in step 4 (as of 2019-05-01). This conversion will require substantial time on a sizeable database. On a PC with an Intel Core i5 CPU using a hard drive and MariaDB 10.1, converting a 3 GB database required 164 minutes. The same database took 3 minutes to convert on a virtual machine with Oracle Linux and MariaDB 10.3. Performing the conversion with phpMyAdmin may cause a PHP timeout. Running the script with the mysql command avoids that:
{CODE(colors="shell" theme="default")}mysql -u userName -p databaseName < db\tiki_convert_myisam_to_innodb.sql{CODE}
Nevertheless, step 4 may fail converting the tiki_files table if innodb_log_file_size is not high enough. In one case, 25 MB was insufficient (80 MB sufficed).

~tc~ THE FOLLOWING SHOULD MOVE TO DEV.TIKI.ORG. Rename of https://dev.tiki.org/ExperimentalBranches+InnoDB to just "InnoDB" requested 2019-04-30. Chealer9 ~/tc~

! Supporting InnoDB
!! Installs
Rules
* No FKs are allowed in the tiki.sql script.
* Fulltext index definitions are placed in the tiki_myisam.sql file. InnoDB specific definitions are placed in the tiki_innodb.sql file.
* The word MyISAM must be used (only) in the engine specification, and it is not allowed in attribute names or other definitions.

The Tiki installer translates the engine type, based on the selected database in the installer GUI.

After the main install script (tiki.sql), the installer will run tiki_myisam.sql or tiki_innodb.sql for the respective installation. tiki_myisam.sql installs the fulltext indexes.

!! Upgrades
When adding an engine-dependent patch, the engine-independent SQL statements must be put in the YYYYMMDD_description_tiki.sql file. The engine-dependent parts must be put in an accompanying PHP file, defining a post_YYYYMMDD_description_tiki function.
Example: Add a table with a fulltext index
{CODE(caption="20110918_tiki_test_tiki.sql" wrap="0")}DROP TABLE IF EXISTS `tiki_test`;
CREATE TABLE `tiki_test` (
  `title` varchar(255) default NULL,
  KEY `title` (`title`)
) ENGINE=MyISAM;{CODE}
and a PHP file specifying the engine dependent part
{CODE(caption="20110918_tiki_test_tiki.php")}function post_20110918_tiki_test_tiki( $installer ) {
  if($installer->isMySQLFulltextSearchSupported()) {
    $installer->query( "CREATE FULLTEXT INDEX ft_test ON tiki_test(`title`);");
  }
}
{CODE}

!! Continuous Integration
The [https://gitlab.com/tikiwiki/tiki/-/blob/master/.gitlab-ci.yml|Tiki CI] has sql-engine-conversion section which leverages doc/devtools/check_sql_engine_conversion.php 

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See also: [https://dev.tiki.org/ExperimentalBranches+InnoDB|ExperimentalBranches InnoDB]