Manual:$wgLegacySchemaConversion

Details
If set to, the MediaWiki 1.4 to 1.5 schema conversion will create stub reference rows in the text table instead of copying the full text of all current entries from 'cur' to 'text'.

This will speed up the conversion step for large sites, but requires that the cur table be kept around for those revisions to remain viewable.

maintenance/migrateCurStubs.php can be used to complete the migration in the background once the wiki is back online.

This option affects the updaters only. Any present cur stub revisions will be readable at runtime regardless of this setting.