As anybody who has ever implemented a Storage Engine for MySQL will know, a bunch of the DDL calls got passed a parameter named “path”. This was a filesystem path. Depending on what platform you were running, it may contain / or \ (and no, it’s not consistent on each platform). Add to that the difference if you were creating temporary tables (table name of #sql_somethingsomething) and the difference if you were one of the two (built in) engines that were able to be used for creating internal temporary tables (temp tables that are created during query execution that do not belong in a schema). Well… you had a bit of a mess.
My earlier attempts involved splitting everything up into two strings: schema name and table name. This ended badly. The final architecture we decided on was to have an object passed around that would deal with various transformations (from what the user entered to what we can store on file systems, or to what temporary table maps to what unique name). This is TableIdentifier.
Brian has been introducing it around the code for a while now, and we just got it to now most of the places where table names are passed to Storage Engines. This means that if you’re writing a Storage Engine that doesn’t just blindly store things in files, you can sensibly use the getSchemaName() and getTableName() methods to call your API.