Implemented auto migration support for appending new columns #2934
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Description of Changes
Previously, you couldn't add new columns at the end of a table without clearing the database, even though this should not require a manual schema change.
API and ABI breaking changes
None.
Expected complexity level and risk
4:
This small change might easily be totally incorrect, possibly overwrite some unrelated data (although all existing tests pass) or collapse the Universe. Need advice from people who understand the inner workings better than your humble.
In particular, how do schema rollbacks handle this?
For adding variants (#2874), new logic had to be introduced. As I suppose, in this case the underlying data store gets duplicated and refilled entirely, rather than altered in-place? If not, perhaps
PendingSchemaChange
needs to be extended as well, with all the hassle this implies.Also, I'm not sure about using
column_id
as position, but the comment in a latter hand is somewhat reassuring.Testing