kaisun2000 commented on a change in pull request #1109:
URL: https://github.com/apache/helix/pull/1109#discussion_r445205072
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -984,11 +997,51 @@ private void fireAllEvents() {
protected List<String> getChildren(final String path, final boolean watch) {
long startT = System.currentTimeMillis();
+
try {
List<String> children = retryUntilConnected(new Callable<List<String>>()
{
+ private int connectionLossRetryCount = 0;
+
@Override
public List<String> call() throws Exception {
- return getConnection().getChildren(path, watch);
+ try {
+ return getConnection().getChildren(path, watch);
+ } catch (ConnectionLossException e) {
+ ++connectionLossRetryCount;
+ // Allow retrying 3 times before checking stat checking number of
children,
+ // because there is a higher possibility that connection loss is
caused by other
+ // factors such as network connectivity, connected ZK node could
not serve
+ // the request, session expired, etc.
+ if (connectionLossRetryCount >= 3) {
+ // Issue: https://github.com/apache/helix/issues/962
+ // Connection loss might be caused by an excessive number of
children.
+ // Infinitely retrying connecting may cause high GC in ZK server
and kill ZK server.
+ // This is a workaround to check numChildren to have a chance to
exit retry loop.
+ // TODO: remove this check once we have a better way to exit
infinite retry
+ Stat stat = getStat(path);
+ if (stat != null) {
+ if (stat.getNumChildren() > NUM_CHILDREN_LIMIT) {
+ LOG.error("Failed to get children for path {} because number
of children {} "
+ + "exceeds limit {}, aborting retry.", path,
stat.getNumChildren(),
+ NUM_CHILDREN_LIMIT);
+ // There is not an accurate KeeperException for the purpose.
+ // MarshallingErrorException could represent transport error,
+ // so use it to exit retry loop and tell that zk is not able
to
+ // transport the data because packet length is too large.
+ throw new KeeperException.MarshallingErrorException();
Review comment:
`If user catches ZkException and handles it, there is extra impact,
their app still runs.`
Do you mean there is **no extra impact?**
Overall, I am a little bit confused. I think ZkException is what we
(IOItech) convert from KeeperException to. Upper layer sees ZkException, they
don't deal with KeeperException (which is from Zookeeper client).
In this case, as long as ZkClient event thread can catch this ZkException
and don't terminate, that is what we want, right?
Am I missing something?
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