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1d6538cd30
When dropping a column from a CDC log table, set the column drop
timestamp several seconds into the future.
If a value is written to a column concurrently with dropping that
column, the value's timestamp may be after the column drop timestamp. If
this value is also flushed to an SSTable, the SSTable would be
corrupted, because it considers the column missing after the drop
timestamp and doesn't allow values for it.
While this issue affects general tables, it especially impacts CDC tables
because this scenario can occur when writing to a table with CDC preimage
enabled while dropping a column from the base table. This happens even if
the base mutation doesn't write to the dropped column, because CDC log
mutations can generate values for a column even if the base mutation doesn't.
For general tables, this issue can be avoided by simply not writing to a
column while dropping it.
We fix this for the more problematic case of CDC log tables by setting
the column drop timestamp several seconds into the future, ensuring that
writes concurrent with column drops are much less likely to have
timestamps greater than the column drop timestamp.
Fixes scylladb/scylladb#26340
(cherry picked from commit 48298e38ab)