dcapwell commented on code in PR #3842:
URL: https://github.com/apache/cassandra/pull/3842#discussion_r1937741779
##########
src/java/org/apache/cassandra/service/accord/AccordConfigurationService.java:
##########
@@ -433,16 +436,25 @@ protected void fetchTopologyInternal(long epoch)
Stage.ACCORD_MIGRATION.execute(() -> {
if (ClusterMetadata.current().epoch.getEpoch() < epoch)
ClusterMetadataService.instance().fetchLogFromCMS(Epoch.create(epoch));
+
+ // In most cases, after fetching log from CMS, we will be caught
up to the required epoch.
+ // This TCM will also notify Accord via reportMetadata, so we do
not need to fetch topologies.
+ // If metadata has reported has skipped one or more epochs, and is
_ahead_ of the requested epoch,
+ // we need to fetch topologies from peers to fill in the gap.
+ ClusterMetadata metadata = ClusterMetadata.current();
+ if (metadata.epoch.getEpoch() == epoch)
+ return;
+
try
{
- Set<InetAddressAndPort> peers = new
HashSet<>(ClusterMetadata.current().directory.allJoinedEndpoints());
+ Set<InetAddressAndPort> peers = new
HashSet<>(metadata.directory.allJoinedEndpoints());
peers.remove(FBUtilities.getBroadcastAddressAndPort());
if (peers.isEmpty())
return;
- Topology topology;
- while ((topology =
FetchTopology.fetch(SharedContext.Global.instance, peers, epoch).get()) == null)
- {
- }
+
+ // TODO (required): fetch only _missing_ topologies.
Review Comment:
one additional optimization... now that we waiting for TCM, TCM might have
already informed us... we could check if accord has this epoch and avoid this.
Maybe add a TODO for that?
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