[jb613]

> and a value that is the configuration object serialized in JSON

It all depends on the data, but if it's not simple, then serialized JSON values would generally incur performance hit for search operations. Breaking out the data into separate columns could be better indexed.

[tigershark]

No, there is no whatsoever performance hit because the identifiers are in separate columns in the same table, and they can be indexed normally. There will be a performance hit if for some future requirement all the ids column are exhausted, they start using the generic key with complex serialized objects AND they want the generic key to be searchable. At that point they can simply add another id column if it is really necessary.