Piotr Szymaniak 38bd068f78 alternator/streams: keep disabled streams usable and purge on re-enable ...

Previously, disabling Alternator Streams would create a blank
cdc::options with only enabled=false, which meant losing access also
to stored Streams's data (including preimage and postimage).

Now, when a stream is disabled:
- The existing CDC options are preserved (only 'enabled' is flipped to
  false), so StreamViewType remains available.
- DescribeStream enumerates all shards with EndingSequenceNumber set,
  indicating they are closed.
- GetRecords omits NextShardIterator for disabled streams.
- DescribeTable (supplement_table_stream_info) reports the stream ARN
  and StreamEnabled: false when the CDC log table still exists.
- ListStreams uses get_base_table instead of is_log_for_some_table so
  that disabled streams whose log table still exists are listed.

When a stream is re-enabled on an Alternator table that has an existing
(disabled) CDC log table, the old log table is dropped and a fresh one
is created with a new UUID, producing a new StreamArn. This is
Alternator-specific behavior; CQL CDC tables continue to reuse the
existing log table.

The old stream data is lost immediately upon re-enable. DynamoDB keeps
it readable for 24 hours.

Tests:
- test_streams_closed_read, test_streams_disabled_stream: remove xfail
  now that disabled streams are usable.
- test_streams_reenable: new test verifying that re-enabling produces
  a new ARN and the old data is still readable via the old ARN (xfail
  because Scylla currently purges old data on re-enable).

Fixes scylladb/scylladb#7239

2026-05-07 14:45:42 +02:00

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