The view builder builds a view by going over the entire token ring,
consuming the base table partitions, and generating view updates for
each partition.
A view is considered as built when we complete a full cycle of the
token ring. Suppose we start to build a view at a token F. We will
consume all partitions with tokens starting at F until the maximum
token, then go back to the minimum token and consume all partitions
until F, and then we detect that we pass F and complete building the
view. This happens in the view builder consumer in
`check_for_built_views`.
The problem is that we check if we pass the first token F with the
condition `_step.current_token() >= it->first_token` whenever we consume
a new partition or the current_token goes back to the minimum token.
But suppose that we don't have any partitions with a token greater than
or equal to the first token (this could happen if the partition with
token F was moved to another node for example), then this condition will never be
satisfied, and we don't detect correctly when we pass F. Instead, we
go back to the minimum token, building the same token ranges again,
in a possibly infinite loop.
To fix this we add another step when reaching the end of the reader's
stream. When this happens it means we don't have any more fragments to
consume until the end of the range, so we advance the current_token to
the end of the range, simulating a partition, and check for built views
in that range.
Fixesscylladb/scylladb#21829Closesscylladb/scylladb#22493
(cherry picked from commit 6d34125eb7)
Closesscylladb/scylladb#22607
58eda6670f