SELECT commands with SERIAL consistency level are historically allowed
for vnode-based views, even though they don't provide linearizability
guarantees. We prohibit LWTs for tablet-based views, but preserve old
behavior for vnode-based view for compatibility. Similar logic is
applied to CDC log tables.
Fixesscylladb/scylladb#26258
Write requests cannot be safely retried if some replicas respond with
accepts and others with rejects. In this case, the coordinator is
uncertain about the outcome of the LWT: a subsequent LWT may either
complete the Paxos round (if a quorum observed the accept) or overwrite it
(if a quorum did not). If the original LWT was actually completed by
later rounds and the coordinator retried it, the write could be applied
twice, potentially overwriting effects of other LWTs that slipped in
between. Read requests do not have this problem, so they
can be safely retried.
Before this commit, handler->accept_proposal was called with
timeout_if_partially_accepted := true. This caused both read and write
requests to throw an "uncertainty" timeout to the user in the case
of the contention described above. After this commit, we throw an
"uncertainty" timeout only for write requests, while read requests
are instead retried in the loop in sp::cas.
Closesscylladb/scylladb#25602
The test_lwt_timeout_while_creating_paxos_state_table was failing after
implementing odd number voter enforcement in the group0 voter calculator.
Previously with 2 nodes:
- 2 nodes → 2 voters → stop 1 node → 1/2 voters (no quorum) → expected Raft timeout
With odd voter count enforcement:
- 2 nodes → 1 voter → stop 1 node → 0/1 voters → Cassandra availability error
This change updates the test to use 3 nodes instead of 2, ensuring proper
no-quorum scenarios:
- 3 nodes → 3 voters → stop 2 nodes → 1/3 voters (no quorum) → Raft timeout
The test now correctly validates LWT timeout behavior while being compatible
with the odd number voter enforcement requirement.
This is a refactoring commit. Remove the rf_rack_valid_keyspaces: False
flag because rf_rack_validy is going to become mundatory in
scylladb/scylladb#23526
This test checks that the paxos state is preserved in case
of tablet rebuild. This happens e.g. when a node is lost
permanently and another node is started to replace it.
LWT is now supported for tablets, but this requires LWT_WITH_TABLETS
feature. We migrate the test so that it checks the error messages in
case the feature is not supported.
This test verifies that Paxos state is correctly migrated when
the base table's tablet is migrated. This test fails if Paxos
state is stored in system.paxos, as the final Paxos read would
reflect conflicting outcomes from both prior LWT operations.
