The actual data: wiki pages, blog posts, files (unless you configure to store in filesystem) etc.
For Tiki data, MyISAM has been used since the beginning of Tiki (2002). In 2017, the default storage engine became InnoDB.
The Unified Index: a copy of your data in a format optimized for search
For the unified index, MyISAM has been used since the beginning of Tiki (2002). In 2024 Tiki28, it becomes InnoDB. As a user, you don't need to configure anything. It is all automatic.
MyISAM still works just fine and will for many years. And you can easily convert later.
Migration steps:
Make sure you are not using the deprecated tiki-searchresults.php feature (preference name feature_search_fulltext and removed after Tiki26), but instead use tiki-searchindex.php (preference name: feature_search)
Do a full backup of your current database/installation
Alter the database engine for all tables to InnoDB using db/tiki_convert_myisam_to_innodb.sql
Performing the conversion with phpMyAdmin may cause a PHP timeout. Running the script with the mysql command avoids that:
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mysql -u userName -p databaseName < db\tiki_convert_myisam_to_innodb.sql
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).