When a materialized view has a key (in Alternator, this can be two
keys) which was a regular column in the base table, and a base
update modifies that regular column, there are two distinct cases:
1. If the old and new key values are different, we need to delete the
old view row, and create a new view row (with the different key).
2. If the old and new key values are the same, we just need to update
the pre-existing row.
It's important not to confuse the two cases: If we try to delete and
create the *same* view row in the same timestamp, the result will be
that the row will be deleted (a tombstone wins over data if they have the
same timestamp) instead of updated. This is what we saw in issue #11801.
We had a bug that was seen when an update set the view key column to
the old value it already had: To compare the old and new key values
we used the function compare_atomic_cell_for_merge(), but this compared
not just they values but also incorrectly compared the metadata such as
a the timestamp. Because setting a column to the same value changes its
timestamp, we wrongly concluded that these to be different view keys
and used the delete-and-create code for this case, resulting in the
view row being deleted (as explained above).
The simple fix is to compare just the key values - not looking at
the metadata.
See tests reproducing this bug and confirming its fix in the next patch.
Fixes#11801
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
8f4243b875