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Comment on the extra reroute after failing shards (#44152) 

The `ShardFailedClusterStateTaskExecutor` fails some shards, which performs a
reroute, but then sometimes schedules a followup reroute. It's not clear from
the code why this followup is necessary, so this commit adds a short comment
describing why it's necessary.
This commit is contained in:
David Turner 2019-07-10 13:23:40 +01:00
parent cad804df92
commit d0f1a756d9
1 changed files with 5 additions and 4 deletions
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9
server/src/main/java/org/elasticsearch/cluster/action/shard/ShardStateAction.java
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@ -378,10 +378,11 @@ public class ShardStateAction {
public void clusterStatePublished(ClusterChangedEvent clusterChangedEvent) {
int numberOfUnassignedShards = clusterChangedEvent.state().getRoutingNodes().unassigned().size();
if (numberOfUnassignedShards > 0) {
String reason = String.format(Locale.ROOT, "[%d] unassigned shards after failing shards", numberOfUnassignedShards);
if (logger.isTraceEnabled()) {
logger.trace("{}, scheduling a reroute", reason);
}
// The reroute called after failing some shards will not assign any shard back to the node on which it failed. If there were
// no other options for a failed shard then it is left unassigned. However, absent other options it's better to try and
// assign it again, even if that means putting it back on the node on which it previously failed:
final String reason = String.format(Locale.ROOT, "[%d] unassigned shards after failing shards", numberOfUnassignedShards);
logger.trace("{}, scheduling a reroute", reason);
rerouteService.reroute(reason, ActionListener.wrap(
r -> logger.trace("{}, reroute completed", reason),
e -> logger.debug(new ParameterizedMessage("{}, reroute failed", reason), e)));