Manual:$wgMultiContentRevisionSchemaMigrationStage

$wgMultiContentRevisionSchemaMigrationStage indicates the RevisionStore table schema migration stage (content, slots, content_models & slot_roles tables). Most wikis can set this to  and run maintenance/migrateXXX.php, the according maintenance script, as soon as any necessary extensions are updated.

Note that reading the old and new schema at the same time is not supported. Attempting to set both read bits in $wgMultiContentRevisionSchemaMigrationStage will result in an InvalidArgumentException.

Details
$wgCommentTableSchemaMigrationStage can be set to one combination of the Schema change migration flags. The allowed value range for the configuration is one of the  constants. The available constants and their planned use cases on Wikimedia Foundation wikis are as follows:
 * (0x03, default value): Only read and write the old schema. The new schema need not even exist. This is used from when the patch is merged until the schema change is actually applied to the database.
 * (0x13): Write both the old and new schema. Read the new schema preferentially, falling back to the old. This is used while the change is being tested, allowing easy roll-back to the old schema.
 * (0x31): Write only the new schema. Read the new schema preferentially, falling back to the old. This is used while running the maintenance script to migrate existing entries in the old schema to the new schema.
 * (0x30): Only read and write the new schema. The old schema (and the feature flag) may now be removed.

For non-Wikimedia Foundation wikis it is recommended to set this to  and to run maintenance/migrateXXX.php in order to take advantage of the new schema.