aweisberg commented on code in PR #4043:
URL: https://github.com/apache/cassandra/pull/4043#discussion_r2027770849
##########
src/java/org/apache/cassandra/service/paxos/v1/PrepareCallback.java:
##########
@@ -79,8 +86,28 @@ public synchronized void onResponse(Message<PrepareResponse>
message)
latch.decrement();
}
- public Iterable<InetAddressAndPort> replicasMissingMostRecentCommit()
+ public Iterable<InetAddressAndPort>
replicasMissingMostRecentCommit(TableMetadata metadata)
{
+ /**
+ * this check is only needed for mixed mode operation with 4.0 and can
be removed once upgrade support dropped
+ * see the comment in {@link
org.apache.cassandra.distributed.upgrade.MixedModePaxosTTLTest} for a full
explanation.
+ */
+ if (DatabaseDescriptor.paxosStatePurging() ==
Config.PaxosStatePurging.legacy)
+ {
+ // In general, we need every replicas that have answered to the
prepare (a quorum) to agree on the MRC (see
+ // coment in StorageProxy.beginAndRepairPaxos(), but basically we
need to make sure at least a quorum of nodes
+ // have learn a commit before commit a new one otherwise that
previous commit is not guaranteed to have reach a
+ // quorum and further commit may proceed on incomplete
information).
+ // However, if that commit is too hold, it may have been expired
from some of the replicas paxos table (we don't
+ // keep the paxos state forever or that could grow unchecked), and
we could end up in some infinite loop as
+ // explained on CASSANDRA-12043. To avoid that, we ignore a MRC
that is too old, i.e. older than the TTL we set
+ // on paxos tables. For such old commit, we rely on hints and
repair to ensure the commit has indeed be
Review Comment:
```suggestion
// on paxos tables. For such an old commit, we rely on hints and
repair to ensure the commit has indeed been
```
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