TYPO3 Core

While one can expect that the default DB connection for a TYPO3 is always available, there are scenarios where additional databases might not be available temporarily. Especially in case of schema migration this can result in problems, e.g. because a "not so important" additional DB should be ignored, while still wanting the schema migration to take place for the default connection.

A common scenario where this could occur is during deployment when and if the EXT:typo3_console command database:updateschema is run.
Currently, running this command with an unavailable additional DB is not possible as an unhandled exception would be thrown before the actual migration, due to the connection timeout.

So there seems to be the general idea there could be a need to be able to "skip" additional databases in some scenarios, most probably (but perhaps in other cases as well) during :

• SchemaMigration

So the database configuration needs to cater for different scenarios:

1. no schema migration should be done (table is completely managed by a 3rd party)
2. schema migration only for mapped tables (in general tables are managed by a 3rd party, but a few tables were created by TYPO3)
3. full schema control (like TYPO3 default, 3rd party tables not mapped should be removed)

While this covers the intended altering of tables, in order to cope with connection issues perhaps additionally

• the schema migration should have an option to skip unavailable connections (handle the exceptions) and still run for the others

Current state is:

• If a table mapping exists, then the whole connection is treated by the SchemaMigration

Some incomplete approaches for the current situation are:

• additional.php: Check if additional condition is up (and perhaps if on CLI), perhaps remove connection.
• read-only user for db access